Methods and compositions for diagnosis and prognosis of renal injury and renal failure

ABSTRACT

The present invention relates to methods and compositions for monitoring, diagnosis, prognosis, and determination of treatment regimens in subjects suffering from or suspected of having a renal injury. In particular, the invention relates to using assays that detect one or more markers selected from the group consisting of cytochrome c and insulin-like growth factor IA as diagnostic and prognostic biomarkers in renal injuries.

The present invention claims priority from U.S. Provisional PatentApplication 61/092,921 filed Aug. 29, 2008, and U.S. Provisional PatentApplication 61/092,918 filed Aug. 29, 2008, each of which is herebyincorporated in its entirety including all tables, figures, and claims.

BACKGROUND OF THE INVENTION

The following discussion of the background of the invention is merelyprovided to aid the reader in understanding the invention and is notadmitted to describe or constitute prior art to the present invention.

The kidney is responsible for water and solute excretion from the body.Its functions include maintenance of acid-base balance, regulation ofelectrolyte concentrations, control of blood volume, and regulation ofblood pressure. As such, loss of kidney function through injury and/ordisease results in substantial morbidity and mortality. A detaileddiscussion of renal injuries is provided in Harrison's Principles ofInternal Medicine, 17^(th) Ed., McGraw Hill, New York, pages 1741-1830,which are hereby incorporated by reference in their entirety. Renaldisease and/or injury may be acute or chronic. Acute and chronic kidneydisease are described as follows (from Current Medical Diagnosis &Treatment 2008, 47^(th) Ed, McGraw Hill, New York, pages 785-815, whichare hereby incorporated by reference in their entirety): “Acute renalfailure is worsening of renal function over hours to days, resulting inthe retention of nitrogenous wastes (such as urea nitrogen) andcreatinine in the blood. Retention of these substances is calledazotemia. Chronic renal failure (chronic kidney disease) results from anabnormal loss of renal function over months to years”.

Acute renal failure (ARF, also known as acute kidney injury, or AKI) isan abrupt (typically detected within about 48 hours to 1 week) reductionin glomerular filtration. This loss of filtration capacity results inretention of nitrogenous (urea and creatinine) and non-nitrogenous wasteproducts that are normally excreted by the kidney, a reduction in urineoutput, or both. It is reported that ARF complicates about 5% ofhospital admissions, 4-15% of cardiopulmonary bypass surgeries, and upto 30% of intensive care admissions. ARF may be categorized as prerenal,intrinsic renal, or postrenal in causation. Intrinsic renal disease canbe further divided into glomerular, tubular, interstitial, and vascularabnormalities. Major causes of ARF are described in the following table,which is adapted from the Merck Manual, 17^(th) ed., Chapter 222, andwhich is hereby incorporated by reference in their entirety:

Type Risk Factors Prerenal ECF volume depletion Excessive diuresis,hemorrhage, GI losses, loss of intravascular fluid into theextravascular space (due to ascites, peritonitis, pancreatitis, orburns), loss of skin and mucus membranes, renal salt- and water-wastingstates Low cardiac output Cardiomyopathy, MI, cardiac tamponade,pulmonary embolism, pulmonary hypertension, positive-pressure mechanicalventilation Low systemic vascular Septic shock, liver failure,antihypertensive drugs resistance Increased renal vascular NSAIDs,cyclosporines, tacrolimus, hypercalcemia, resistance anaphylaxis,anesthetics, renal artery obstruction, renal vein thrombosis, sepsis,hepatorenal syndrome Decreased efferent ACE inhibitors or angiotensin IIreceptor blockers arteriolar tone (leading to decreased GFR from reducedglomerular transcapillary pressure, especially in patients withbilateral renal artery stenosis) Intrinsic Renal Acute tubular injuryIschemia (prolonged or severe prerenal state): surgery, hemorrhage,arterial or venous obstruction; Toxins: NSAIDs, cyclosporines,tacrolimus, aminoglycosides, foscarnet, ethylene glycol, hemoglobin,myoglobin, ifosfamide, heavy metals, methotrexate, radiopaque contrastagents, streptozotocin Acute glomerulonephritis ANCA-associated:Crescentic glomerulonephritis, polyarteritis nodosa, Wegener'sgranulomatosis; Anti- GBM glomerulonephritis: Goodpasture's syndrome;Immune-complex: Lupus glomerulonephritis, postinfectiousglomerulonephritis, cryoglobulinemic glomerulonephritis Acutetubulointerstitial Drug reaction (eg, β-lactams, NSAIDs, sulfonamides,nephritis ciprofloxacin, thiazide diuretics, furosemide, phenytoin,allopurinol, pyelonephritis, papillary necrosis Acute vascularVasculitis, malignant hypertension, thrombotic nephropathymicroangiopathies, scleroderma, atheroembolism Infiltrative diseasesLymphoma, sarcoidosis, leukemia Postrenal Tubular precipitation Uricacid (tumor lysis), sulfonamides, triamterene, acyclovir, indinavir,methotrexate, ethylene glycol ingestion, myeloma protein, myoglobinUreteral obstruction Intrinsic: Calculi, clots, sloughed renal tissue,fungus ball, edema, malignancy, congenital defects; Extrinsic:Malignancy, retroperitoneal fibrosis, ureteral trauma during surgery orhigh impact injury Bladder obstruction Mechanical: Benign prostatichyperplasia, prostate cancer, bladder cancer, urethral strictures,phimosis, paraphimosis, urethral valves, obstructed indwelling urinarycatheter; Neurogenic: Anticholinergic drugs, upper or lower motor neuronlesion

In the case of ischemic ARF, the course of the disease may be dividedinto four phases. During an initiation phase, which lasts hours to days,reduced perfusion of the kidney is evolving into injury. Glomerularultrafiltration reduces, the flow of filtrate is reduced due to debriswithin the tubules, and back leakage of filtrate through injuredepithelium occurs. Renal injury can be mediated during this phase byreperfusion of the kidney. Initiation is followed by an extension phasewhich is characterized by continued ischemic injury and inflammation andmay involve endothelial damage and vascular congestion. During themaintenance phase, lasting from 1 to 2 weeks, renal cell injury occurs,and glomerular filtration and urine output reaches a minimum. A recoveryphase can follow in which the renal epithelium is repaired and GFRgradually recovers. Despite this, the survival rate of subjects with ARFmay be as low as about 60%.

Acute kidney injury caused by radiocontrast agents (also called contrastmedia) and other nephrotoxins such as cyclosporine, antibioticsincluding aminoglycosides and anticancer drugs such as cisplatinmanifests over a period of days to about a week. Contrast inducednephropathy (CIN, which is AKI caused by radiocontrast agents) isthought to be caused by intrarenal vasoconstriction (leading to ischemicinjury) and from the generation of reactive oxygen species that aredirectly toxic to renal tubular epithelial cells. CIN classicallypresents as an acute (onset within 24-48 h) but reversible (peak 3-5days, resolution within 1 week) rise in blood urea nitrogen and serumcreatinine.

A commonly reported criteria for defining and detecting AKI is an abrupt(typically within about 2-7 days or within a period of hospitalization)elevation of serum creatinine. Although the use of serum creatinineelevation to define and detect AKI is well established, the magnitude ofthe serum creatinine elevation and the time over which it is measured todefine AKI varies considerably among publications. Traditionally,relatively large increases in serum creatinine such as 100%, 200%, anincrease of at least 100% to a value over 2 mg/dL and other definitionswere used to define AKI. However, the recent trend has been towardsusing smaller serum creatinine rises to define AKI. The relationshipbetween serum creatinine rise, AKI and the associated health risks arereviewed in Praught and Shlipak, Curr Opin Nephrol Hypertens 14:265-270,2005 and Chertow et al, J Am Soc Nephrol 16: 3365-3370, 2005, which,with the references listed therein, are hereby incorporated by referencein their entirety. As described in these publications, acute worseningrenal function (AKI) and increased risk of death and other detrimentaloutcomes are now known to be associated with very small increases inserum creatinine. These increases may be determined as a relative(percent) value or a nominal value. Relative increases in serumcreatinine as small as 20% from the pre-injury value have been reportedto indicate acutely worsening renal function (AKI) and increased healthrisk, but the more commonly reported value to define AKI and increasedhealth risk is a relative increase of at least 25%. Nominal increases assmall as 0.3 mg/dL, 0.2 mg/dL or even 0.1 mg/dL have been reported toindicate worsening renal function and increased risk of death. Varioustime periods for the serum creatinine to rise to these threshold valueshave been used to define AKI, for example, ranging from 2 days, 3 days,7 days, or a variable period defined as the time the patient is in thehospital or intensive care unit. These studies indicate there is not aparticular threshold serum creatinine rise (or time period for the rise)for worsening renal function or AKI, but rather a continuous increase inrisk with increasing magnitude of serum creatinine rise.

One study (Lassnigg et all, J Am Soc Nephrol 15:1597-1605, 2004, herebyincorporated by reference in its entirety) investigated both increasesand decreases in serum creatinine. Patients with a mild fall in serumcreatinine of −0.1 to −0.3 mg/dL following heart surgery had the lowestmortality rate. Patients with a larger fall in serum creatinine (morethan or equal to −0.4 mg/dL) or any increase in serum creatinine had alarger mortality rate. These findings caused the authors to concludethat even very subtle changes in renal function (as detected by smallcreatinine changes within 48 hours of surgery) seriously effectpatient's outcomes. In an effort to reach consensus on a unifiedclassification system for using serum creatinine to define AKI inclinical trials and in clinical practice, Bellomo et al., Crit Care.8(4):R204-12, 2004, which is hereby incorporated by reference in itsentirety, proposes the following classifications for stratifying AKIpatients:

“Risk”: serum creatinine increased 1.5 fold from baseline OR urineproduction of <0.5 ml/kg body weight/hr for 6 hours;“Injury”: serum creatinine increased 2.0 fold from baseline OR urineproduction <0.5 ml/kg/hr for 12 h;“Failure”: serum creatinine increased 3.0 fold from baseline ORcreatinine >355 μmol/l (with a rise of >44) or urine output below 0.3ml/kg/hr for 24 h or anuria for at least 12 hours;And included two clinical outcomes:“Loss”: persistent need for renal replacement therapy for more than fourweeks.“ESRD”: end stage renal disease—the need for dialysis for more than 3months.These criteria are called the RIFLE criteria, which provide a usefulclinical tool to classify renal status. As discussed in Kellum, Crit.Care Med. 36: S141-45, 2008 and Ricci et al., Kidney Int. 73, 538-546,2008, each hereby incorporated by reference in its entirety, the RIFLEcriteria provide a uniform definition of AKI which has been validated innumerous studies.

More recently, Mehta et al., Crit. Care 11:R31 (doi:10.1186.cc5713),2007, hereby incorporated by reference in its entirety, proposes thefollowing similar classifications for stratifying AKI patients, whichhave been modified from RIFLE:

“Stage I”: increase in serum creatinine of more than or equal to 0.3mg/dL (≧26.4 μmol/L) or increase to more than or equal to 150%(1.5-fold) from baseline OR urine output less than 0.5 mL/kg per hourfor more than 6 hours;“Stage II”: increase in serum creatinine to more than 200% (>2-fold)from baseline OR urine output less than 0.5 mL/kg per hour for more than12 hours;“Stage III”: increase in serum creatinine to more than 300% (>3-fold)from baseline OR serum creatinine >354 μmol/L accompanied by an acuteincrease of at least 44 μmol/L OR urine output less than 0.3 mL/kg perhour for 24 hours or anuria for 12 hours.

The CIN Consensus Working Panel (McCollough et al, Rev Cardiovasc Med.2006; 7(4):177-197, hereby incorporated by reference in its entirety)uses a serum creatinine rise of 25% to define Contrast inducednephropathy (which is a type of AKI).Although various groups proposeslightly different criteria for using serum creatinine to detect AKI,the consensus is that small changes in serum creatinine, such as 0.3mg/dL or 25%, are sufficient to detect AKI (worsening renal function)and that the magnitude of the serum creatinine change is an indicator ofthe severity of the AKI and mortality risk.

Although serial measurement of serum creatinine over a period of days isan accepted method of detecting and diagnosing AKI and is considered oneof the most important tools to evaluate AKI patients, serum creatinineis generally regarded to have several limitations in the diagnosis,assessment and monitoring of AKI patients. The time period for serumcreatinine to rise to values (e.g., a 0.3 mg/dL or 25% rise) considereddiagnostic for AKI can be 48 hours or longer depending on the definitionused. Since cellular injury in AKI can occur over a period of hours,serum creatinine elevations detected at 48 hours or longer can be a lateindicator of injury, and relying on serum creatinine can thus delaydiagnosis of AKI. Furthermore, serum creatinine is not a good indicatorof the exact kidney status and treatment needs during the most acutephases of AKI when kidney function is changing rapidly. Some patientswith AKI will recover fully, some will need dialysis (either short termor long term) and some will have other detrimental outcomes includingdeath, major adverse cardiac events and chronic kidney disease. Becauseserum creatinine is a marker of filtration rate, it does notdifferentiate between the causes of AKI (pre-renal, intrinsic renal,post-renal obstruction, atheroembolic, etc) or the category or locationof injury in intrinsic renal disease (for example, tubular, glomerularor interstitial in origin). Urine output is similarly limited, Knowingthese things can be of vital importance in managing and treatingpatients with AKI.

These limitations underscore the need for better methods to detect andassess AKI, particularly in the early and subclinical stages, but alsoin later stages when recovery and repair of the kidney can occur.Furthermore, there is a need to better identify patients who are at riskof having an AKI.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide methods and compositions forevaluating renal function in a subject. As described herein, measurementof one or more markers selected from the group consisting of cytochromec and insulin-like growth factor IA (collectively referred to herein as“kidney injury markers, and individually as a “kidney injury marker”)can be used for diagnosis, prognosis, risk stratification, staging,monitoring, categorizing and determination of further diagnosis andtreatment regimens in subjects suffering or at risk of suffering from aninjury to renal function, reduced renal function, and/or acute renalfailure (also called acute kidney injury).

These kidney injury markers may be used, individually or in panelscomprising a plurality of kidney injury markers, for risk stratification(that is, to identify subjects at risk for a future injury to renalfunction, for future progression to reduced renal function, for futureprogression to ARF, for future improvement in renal function, etc.); fordiagnosis of existing disease (that is, to identify subjects who havesuffered an injury to renal function, who have progressed to reducedrenal function, who have progressed to ARF, etc.); for monitoring fordeterioration or improvement of renal function; and for predicting afuture medical outcome, such as improved or worsening renal function, adecreased or increased mortality risk, a decreased or increased riskthat a subject will require renal replacement therapy (i.e.,hemodialysis, peritoneal dialysis, hemofiltration, and/or renaltransplantation, a decreased or increased risk that a subject willrecover from an injury to renal function, a decreased or increased riskthat a subject will recover from ARF, a decreased or increased risk thata subject will progress to end stage renal disease, a decreased orincreased risk that a subject will progress to chronic renal failure, adecreased or increased risk that a subject will suffer rejection of atransplanted kidney, etc.

In a first aspect, the present invention relates to methods forevaluating renal status in a subject. These methods comprise performingan assay method that is configured to detect one or more kidney injurymarkers of the present invention in a body fluid sample obtained fromthe subject. The assay result(s), for example a measured concentrationof one or more markers selected from the group consisting of cytochromec and insulin-like growth factor IA is/are then correlated to the renalstatus of the subject. This correlation to renal status may includecorrelating the assay result(s) to one or more of risk stratification,diagnosis, prognosis, staging, classifying and monitoring of the subjectas described herein. Thus, the present invention utilizes one or morekidney injury markers of the present invention for the evaluation ofrenal injury.

In certain embodiments, the methods for evaluating renal statusdescribed herein are methods for risk stratification of the subject;that is, assigning a likelihood of one or more future changes in renalstatus to the subject. In these embodiments, the assay result(s) is/arecorrelated to one or more such future changes. The following arepreferred risk stratification embodiments.

In preferred risk stratification embodiments, these methods comprisedetermining a subject's risk for a future injury to renal function, andthe assay result(s) is/are correlated to a likelihood of such a futureinjury to renal function. For example, the measured concentration(s) mayeach be compared to a threshold value. For a “positive going” kidneyinjury marker, an increased likelihood of suffering a future injury torenal function is assigned to the subject when the measuredconcentration is above the threshold, relative to a likelihood assignedwhen the measured concentration is below the threshold. For a “negativegoing” kidney injury marker, an increased likelihood of suffering afuture injury to renal function is assigned to the subject when themeasured concentration is below the threshold, relative to a likelihoodassigned when the measured concentration is above the threshold.

In other preferred risk stratification embodiments, these methodscomprise determining a subject's risk for future reduced renal function,and the assay result(s) is/are correlated to a likelihood of suchreduced renal function. For example, the measured concentrations mayeach be compared to a threshold value. For a “positive going” kidneyinjury marker, an increased likelihood of suffering a future reducedrenal function is assigned to the subject when the measuredconcentration is above the threshold, relative to a likelihood assignedwhen the measured concentration is below the threshold. For a “negativegoing” kidney injury marker, an increased likelihood of future reducedrenal function is assigned to the subject when the measuredconcentration is below the threshold, relative to a likelihood assignedwhen the measured concentration is above the threshold.

In still other preferred risk stratification embodiments, these methodscomprise determining a subject's likelihood for a future improvement inrenal function, and the assay result(s) is/are correlated to alikelihood of such a future improvement in renal function. For example,the measured concentration(s) may each be compared to a threshold value.For a “positive going” kidney injury marker, an increased likelihood ofa future improvement in renal function is assigned to the subject whenthe measured concentration is below the threshold, relative to alikelihood assigned when the measured concentration is above thethreshold. For a “negative going” kidney injury marker, an increasedlikelihood of a future improvement in renal function is assigned to thesubject when the measured concentration is above the threshold, relativeto a likelihood assigned when the measured concentration is below thethreshold.

In yet other preferred risk stratification embodiments, these methodscomprise determining a subject's risk for progression to ARF, and theresult(s) is/are correlated to a likelihood of such progression to ARF.For example, the measured concentration(s) may each be compared to athreshold value. For a “positive going” kidney injury marker, anincreased likelihood of progression to ARF is assigned to the subjectwhen the measured concentration is above the threshold, relative to alikelihood assigned when the measured concentration is below thethreshold. For a “negative going” kidney injury marker, an increasedlikelihood of progression to ARF is assigned to the subject when themeasured concentration is below the threshold, relative to a likelihoodassigned when the measured concentration is above the threshold.

And in other preferred risk stratification embodiments, these methodscomprise determining a subject's outcome risk, and the assay result(s)is/are correlated to a likelihood of the occurrence of a clinicaloutcome related to a renal injury suffered by the subject. For example,the measured concentration(s) may each be compared to a threshold value.For a “positive going” kidney injury marker, an increased likelihood ofone or more of: acute kidney injury, progression to a worsening stage ofAKI, mortality, a requirement for renal replacement therapy, arequirement for withdrawal of renal toxins, end stage renal disease,heart failure, stroke, myocardial infarction, progression to chronickidney disease, etc., is assigned to the subject when the measuredconcentration is above the threshold, relative to a likelihood assignedwhen the measured concentration is below the threshold. For a “negativegoing” kidney injury marker, an increased likelihood of one or more of:acute kidney injury, progression to a worsening stage of AKI, mortality,a requirement for renal replacement therapy, a requirement forwithdrawal of renal toxins, end stage renal disease, heart failure,stroke, myocardial infarction, progression to chronic kidney disease,etc., is assigned to the subject when the measured concentration isbelow the threshold, relative to a likelihood assigned when the measuredconcentration is above the threshold.

In such risk stratification embodiments, preferably the likelihood orrisk assigned is that an event of interest is more or less likely tooccur within 180 days of the time at which the body fluid sample isobtained from the subject. In particularly preferred embodiments, thelikelihood or risk assigned relates to an event of interest occurringwithin a shorter time period such as 18 months, 120 days, 90 days, 60days, 45 days, 30 days, 21 days, 14 days, 7 days, 5 days, 96 hours, 72hours, 48 hours, 36 hours, 24 hours, 12 hours, or less. A risk at 0hours of the time at which the body fluid sample is obtained from thesubject is equivalent to diagnosis of a current condition.

In preferred risk stratification embodiments, the subject is selectedfor risk stratification based on the pre-existence in the subject of oneor more known risk factors for prerenal, intrinsic renal, or postrenalARF. For example, a subject undergoing or having undergone majorvascular surgery, coronary artery bypass, or other cardiac surgery; asubject having pre-existing congestive heart failure, preeclampsia,eclampsia, diabetes mellitus, hypertension, coronary artery disease,proteinuria, renal insufficiency, glomerular filtration below the normalrange, cirrhosis, serum creatinine above the normal range, or sepsis; ora subject exposed to NSAIDs, cyclosporines, tacrolimus, aminoglycosides,foscarnet, ethylene glycol, hemoglobin, myoglobin, ifosfamide, heavymetals, methotrexate, radiopaque contrast agents, or streptozotocin areall preferred subjects for monitoring risks according to the methodsdescribed herein. This list is not meant to be limiting. By“pre-existence” in this context is meant that the risk factor exists atthe time the body fluid sample is obtained from the subject. Inparticularly preferred embodiments, a subject is chosen for riskstratification based on an existing diagnosis of injury to renalfunction, reduced renal function, or ARF.

In other embodiments, the methods for evaluating renal status describedherein are methods for diagnosing a renal injury in the subject; thatis, assessing whether or not a subject has suffered from an injury torenal function, reduced renal function, or ARF. In these embodiments,the assay result(s), for example a measured concentration of one or moremarkers selected from the group consisting of cytochrome c andinsulin-like growth factor IA is/are correlated to the occurrence ornonoccurrence of a change in renal status. The following are preferreddiagnostic embodiments.

In preferred diagnostic embodiments, these methods comprise diagnosingthe occurrence or nonoccurrence of an injury to renal function, and theassay result(s) is/are correlated to the occurrence or nonoccurrence ofsuch an injury. For example, each of the measured concentration(s) maybe compared to a threshold value. For a positive going marker, anincreased likelihood of the occurrence of an injury to renal function isassigned to the subject when the measured concentration is above thethreshold (relative to the likelihood assigned when the measuredconcentration is below the threshold); alternatively, when the measuredconcentration is below the threshold, an increased likelihood of thenonoccurrence of an injury to renal function may be assigned to thesubject (relative to the likelihood assigned when the measuredconcentration is above the threshold). For a negative going marker, anincreased likelihood of the occurrence of an injury to renal function isassigned to the subject when the measured concentration is below thethreshold (relative to the likelihood assigned when the measuredconcentration is above the threshold); alternatively, when the measuredconcentration is above the threshold, an increased likelihood of thenonoccurrence of an injury to renal function may be assigned to thesubject (relative to the likelihood assigned when the measuredconcentration is below the threshold).

In other preferred diagnostic embodiments, these methods comprisediagnosing the occurrence or nonoccurrence of reduced renal function,and the assay result(s) is/are correlated to the occurrence ornonoccurrence of an injury causing reduced renal function. For example,each of the measured concentration(s) may be compared to a thresholdvalue. For a positive going marker, an increased likelihood of theoccurrence of an injury causing reduced renal function is assigned tothe subject when the measured concentration is above the threshold(relative to the likelihood assigned when the measured concentration isbelow the threshold); alternatively, when the measured concentration isbelow the threshold, an increased likelihood of the nonoccurrence of aninjury causing reduced renal function may be assigned to the subject(relative to the likelihood assigned when the measured concentration isabove the threshold). For a negative going marker, an increasedlikelihood of the occurrence of an injury causing reduced renal functionis assigned to the subject when the measured concentration is below thethreshold (relative to the likelihood assigned when the measuredconcentration is above the threshold); alternatively, when the measuredconcentration is above the threshold, an increased likelihood of thenonoccurrence of an injury causing reduced renal function may beassigned to the subject (relative to the likelihood assigned when themeasured concentration is below the threshold).

In yet other preferred diagnostic embodiments, these methods comprisediagnosing the occurrence or nonoccurrence of ARF, and the assayresult(s) is/are correlated to the occurrence or nonoccurrence of aninjury causing ARF. For example, each of the measured concentration(s)may be compared to a threshold value. For a positive going marker, anincreased likelihood of the occurrence of ARF is assigned to the subjectwhen the measured concentration is above the threshold (relative to thelikelihood assigned when the measured concentration is below thethreshold); alternatively, when the measured concentration is below thethreshold, an increased likelihood of the nonoccurrence of ARF may beassigned to the subject (relative to the likelihood assigned when themeasured concentration is above the threshold). For a negative goingmarker, an increased likelihood of the occurrence of ARF is assigned tothe subject when the measured concentration is below the threshold(relative to the likelihood assigned when the measured concentration isabove the threshold); alternatively, when the measured concentration isabove the threshold, an increased likelihood of the nonoccurrence of ARFmay be assigned to the subject (relative to the likelihood assigned whenthe measured concentration is below the threshold).

In still other preferred diagnostic embodiments, these methods comprisediagnosing a subject as being in need of renal replacement therapy, andthe assay result(s) is/are correlated to a need for renal replacementtherapy. For example, each of the measured concentration(s) may becompared to a threshold value. For a positive going marker, an increasedlikelihood of the occurrence of an injury creating a need for renalreplacement therapy is assigned to the subject when the measuredconcentration is above the threshold (relative to the likelihoodassigned when the measured concentration is below the threshold);alternatively, when the measured concentration is below the threshold,an increased likelihood of the nonoccurrence of an injury creating aneed for renal replacement therapy may be assigned to the subject(relative to the likelihood assigned when the measured concentration isabove the threshold). For a negative going marker, an increasedlikelihood of the occurrence of an injury creating a need for renalreplacement therapy is assigned to the subject when the measuredconcentration is below the threshold (relative to the likelihoodassigned when the measured concentration is above the threshold);alternatively, when the measured concentration is above the threshold,an increased likelihood of the nonoccurrence of an injury creating aneed for renal replacement therapy may be assigned to the subject(relative to the likelihood assigned when the measured concentration isbelow the threshold).

In still other preferred diagnostic embodiments, these methods comprisediagnosing a subject as being in need of renal transplantation, and theassay result(s) is/are correlated to a need for renal transplantation.For example, each of the measured concentration(s) may be compared to athreshold value. For a positive going marker, an increased likelihood ofthe occurrence of an injury creating a need for renal transplantation isassigned to the subject when the measured concentration is above thethreshold (relative to the likelihood assigned when the measuredconcentration is below the threshold); alternatively, when the measuredconcentration is below the threshold, an increased likelihood of thenonoccurrence of an injury creating a need for renal transplantation maybe assigned to the subject (relative to the likelihood assigned when themeasured concentration is above the threshold). For a negative goingmarker, an increased likelihood of the occurrence of an injury creatinga need for renal transplantation is assigned to the subject when themeasured concentration is below the threshold (relative to thelikelihood assigned when the measured concentration is above thethreshold); alternatively, when the measured concentration is above thethreshold, an increased likelihood of the nonoccurrence of an injurycreating a need for renal transplantation may be assigned to the subject(relative to the likelihood assigned when the measured concentration isbelow the threshold).

In still other embodiments, the methods for evaluating renal statusdescribed herein are methods for monitoring a renal injury in thesubject; that is, assessing whether or not renal function is improvingor worsening in a subject who has suffered from an injury to renalfunction, reduced renal function, or ARF. In these embodiments, theassay result(s), for example a measured concentration of one or moremarkers selected from the group consisting of cytochrome c andinsulin-like growth factor IA is/are correlated to the occurrence ornonoccurrence of a change in renal status. The following are preferredmonitoring embodiments.

In preferred monitoring embodiments, these methods comprise monitoringrenal status in a subject suffering from an injury to renal function,and the assay result(s) is/are correlated to the occurrence ornonoccurrence of a change in renal status in the subject. For example,the measured concentration(s) may be compared to a threshold value. Fora positive going marker, when the measured concentration is above thethreshold, a worsening of renal function may be assigned to the subject;alternatively, when the measured concentration is below the threshold,an improvement of renal function may be assigned to the subject. For anegative going marker, when the measured concentration is below thethreshold, a worsening of renal function may be assigned to the subject;alternatively, when the measured concentration is above the threshold,an improvement of renal function may be assigned to the subject.

In other preferred monitoring embodiments, these methods comprisemonitoring renal status in a subject suffering from reduced renalfunction, and the assay result(s) is/are correlated to the occurrence ornonoccurrence of a change in renal status in the subject. For example,the measured concentration(s) may be compared to a threshold value. Fora positive going marker, when the measured concentration is above thethreshold, a worsening of renal function may be assigned to the subject;alternatively, when the measured concentration is below the threshold,an improvement of renal function may be assigned to the subject. For anegative going marker, when the measured concentration is below thethreshold, a worsening of renal function may be assigned to the subject;alternatively, when the measured concentration is above the threshold,an improvement of renal function may be assigned to the subject.

In yet other preferred monitoring embodiments, these methods comprisemonitoring renal status in a subject suffering from acute renal failure,and the assay result(s) is/are correlated to the occurrence ornonoccurrence of a change in renal status in the subject. For example,the measured concentration(s) may be compared to a threshold value. Fora positive going marker, when the measured concentration is above thethreshold, a worsening of renal function may be assigned to the subject;alternatively, when the measured concentration is below the threshold,an improvement of renal function may be assigned to the subject. For anegative going marker, when the measured concentration is below thethreshold, a worsening of renal function may be assigned to the subject;alternatively, when the measured concentration is above the threshold,an improvement of renal function may be assigned to the subject.

In other additional preferred monitoring embodiments, these methodscomprise monitoring renal status in a subject at risk of an injury torenal function due to the pre-existence of one or more known riskfactors for prerenal, intrinsic renal, or postrenal ARF, and the assayresult(s) is/are correlated to the occurrence or nonoccurrence of achange in renal status in the subject. For example, the measuredconcentration(s) may be compared to a threshold value. For a positivegoing marker, when the measured concentration is above the threshold, aworsening of renal function may be assigned to the subject;alternatively, when the measured concentration is below the threshold,an improvement of renal function may be assigned to the subject. For anegative going marker, when the measured concentration is below thethreshold, a worsening of renal function may be assigned to the subject;alternatively, when the measured concentration is above the threshold,an improvement of renal function may be assigned to the subject.

In still other embodiments, the methods for evaluating renal statusdescribed herein are methods for classifying a renal injury in thesubject; that is, determining whether a renal injury in a subject isprerenal, intrinsic renal, or postrenal; and/or further subdividingthese classes into subclasses such as acute tubular injury, acuteglomerulonephritis acute tubulointerstitial nephritis, acute vascularnephropathy, or infiltrative disease; and/or assigning a likelihood thata subject will progress to a particular RIFLE stage. In theseembodiments, the assay result(s), for example a measured concentrationof one or more markers selected from the group consisting of is/arecorrelated to a particular class and/or subclass. The following arepreferred classification embodiments.

In preferred classification embodiments, these methods comprisedetermining whether a renal injury in a subject is prerenal, intrinsicrenal, or postrenal; and/or further subdividing these classes intosubclasses such as acute tubular injury, acute glomerulonephritis acutetubulointerstitial nephritis, acute vascular nephropathy, orinfiltrative disease; and/or assigning a likelihood that a subject willprogress to a particular RIFLE stage, and the assay result(s) is/arecorrelated to the injury classification for the subject. For example,the measured concentration may be compared to a threshold value, andwhen the measured concentration is above the threshold, a particularclassification is assigned; alternatively, when the measuredconcentration is below the threshold, a different classification may beassigned to the subject.

A variety of methods may be used by the skilled artisan to arrive at adesired threshold value for use in these methods. For example, thethreshold value may be determined from a population of normal subjectsby selecting a concentration representing the 75^(th), 85^(th), 90^(th),95^(th), or 99^(th) percentile of a kidney injury marker measured insuch normal subjects. Alternatively, the threshold value may bedetermined from a “diseased” population of subjects, e.g., thosesuffering from an injury or having a predisposition for an injury (e.g.,progression to ARF or some other clinical outcome such as death,dialysis, renal transplantation, etc.), by selecting a concentrationrepresenting the 75^(th), 85^(th), 90^(th), 95^(th), or 99^(th)percentile of a kidney injury marker measured in such subjects. Inanother alternative, the threshold value may be determined from a priormeasurement of a kidney injury marker in the same subject; that is, atemporal change in the level of a kidney injury marker in the subjectmay be used to assign risk to the subject.

The foregoing discussion is not meant to imply, however, that the kidneyinjury markers of the present invention must be compared tocorresponding individual thresholds. Methods for combining assay resultscan comprise the use of multivariate logistical regression, loglinearmodeling, neural network analysis, n-of-m analysis, decision treeanalysis, calculating ratios of markers, etc. This list is not meant tobe limiting. In these methods, a composite result which is determined bycombining individual markers may be treated as if it is itself a marker;that is, a threshold may be determined for the composite result asdescribed herein for individual markers, and the composite result for anindividual patient compared to this threshold.

The ability of a particular test to distinguish two populations can beestablished using ROC analysis. For example, ROC curves established froma “first” subpopulation which is predisposed to one or more futurechanges in renal status, and a “second” subpopulation which is not sopredisposed can be used to calculate a ROC curve, and the area under thecurve provides a measure of the quality of the test. Preferably, thetests described herein provide a ROC curve area greater than 0.5,preferably at least 0.6, more preferably 0.7, still more preferably atleast 0.8, even more preferably at least 0.9, and most preferably atleast 0.95.

In certain aspects, the measured concentration of one or more kidneyinjury markers, or a composite of such markers, may be treated ascontinuous variables. For example, any particular concentration can beconverted into a corresponding probability of a future reduction inrenal function for the subject, the occurrence of an injury, aclassification, etc. In yet another alternative, a threshold that canprovide an acceptable level of specificity and sensitivity in separatinga population of subjects into “bins” such as a “first” subpopulation(e.g., which is predisposed to one or more future changes in renalstatus, the occurrence of an injury, a classification, etc.) and a“second” subpopulation which is not so predisposed. A threshold value isselected to separate this first and second population by one or more ofthe following measures of test accuracy:

an odds ratio greater than 1, preferably at least about 2 or more orabout 0.5 or less, more preferably at least about 3 or more or about0.33 or less, still more preferably at least about 4 or more or about0.25 or less, even more preferably at least about 5 or more or about 0.2or less, and most preferably at least about 10 or more or about 0.1 orless;a specificity of greater than 0.5, preferably at least about 0.6, morepreferably at least about 0.7, still more preferably at least about 0.8,even more preferably at least about 0.9 and most preferably at leastabout 0.95, with a corresponding sensitivity greater than 0.2,preferably greater than about 0.3, more preferably greater than about0.4, still more preferably at least about 0.5, even more preferablyabout 0.6, yet more preferably greater than about 0.7, still morepreferably greater than about 0.8, more preferably greater than about0.9, and most preferably greater than about 0.95;a sensitivity of greater than 0.5, preferably at least about 0.6, morepreferably at least about 0.7, still more preferably at least about 0.8,even more preferably at least about 0.9 and most preferably at leastabout 0.95, with a corresponding specificity greater than 0.2,preferably greater than about 0.3, more preferably greater than about0.4, still more preferably at least about 0.5, even more preferablyabout 0.6, yet more preferably greater than about 0.7, still morepreferably greater than about 0.8, more preferably greater than about0.9, and most preferably greater than about 0.95;at least about 75% sensitivity, combined with at least about 75%specificity;a positive likelihood ratio (calculated as sensitivity/(1-specificity))of greater than 1, at least about 2, more preferably at least about 3,still more preferably at least about 5, and most preferably at leastabout 10; ora negative likelihood ratio (calculated as (1-sensitivity)/specificity)of less than 1, less than or equal to about 0.5, more preferably lessthan or equal to about 0.3, and most preferably less than or equal toabout 0.1.The term “about” in the context of any of the above measurements refersto +/−5% of a given measurement.

Multiple thresholds may also be used to assess renal status in asubject. For example, a “first” subpopulation which is predisposed toone or more future changes in renal status, the occurrence of an injury,a classification, etc., and a “second” subpopulation which is not sopredisposed can be combined into a single group. This group is thensubdivided into three or more equal parts (known as tertiles, quartiles,quintiles, etc., depending on the number of subdivisions). An odds ratiois assigned to subjects based on which subdivision they fall into. Ifone considers a tertile, the lowest or highest tertile can be used as areference for comparison of the other subdivisions. This referencesubdivision is assigned an odds ratio of 1. The second tertile isassigned an odds ratio that is relative to that first tertile. That is,someone in the second tertile might be 3 times more likely to suffer oneor more future changes in renal status in comparison to someone in thefirst tertile. The third tertile is also assigned an odds ratio that isrelative to that first tertile.

In certain embodiments, the assay method is an immunoassay. Antibodiesfor use in such assays will specifically bind a full length kidneyinjury marker of interest, and may also bind one or more polypeptidesthat are “related” thereto, as that term is defined hereinafter.Numerous immunoassay formats are known to those of skill in the art.Preferred body fluid samples are selected from the group consisting ofurine, blood, serum, saliva, tears, and plasma.

The foregoing method steps should not be interpreted to mean that thekidney injury marker assay result(s) is/are used in isolation in themethods described herein. Rather, additional variables or other clinicalindicia may be included in the methods described herein. For example, arisk stratification, diagnostic, classification, monitoring, etc. methodmay combine the assay result(s) with one or more variables measured forthe subject selected from the group consisting of demographicinformation (e.g., weight, sex, age, race), medical history (e.g.,family history, type of surgery, pre-existing disease such as aneurism,congestive heart failure, preeclampsia, eclampsia, diabetes mellitus,hypertension, coronary artery disease, proteinuria, renal insufficiency,or sepsis, type of toxin exposure such as NSAIDs, cyclosporines,tacrolimus, aminoglycosides, foscarnet, ethylene glycol, hemoglobin,myoglobin, ifosfamide, heavy metals, methotrexate, radiopaque contrastagents, or streptozotocin), clinical variables (e.g., blood pressure,temperature, respiration rate), risk scores (APACHE score, PREDICTscore, TIMI Risk Score for UA/NSTEMI, Framingham Risk Score), aglomerular filtration rate, an estimated glomerular filtration rate, aurine production rate, a serum or plasma creatinine concentration, aurine creatinine concentration, a fractional excretion of sodium, aurine sodium concentration, a urine creatinine to serum or plasmacreatinine ratio, a urine specific gravity, a urine osmolality, a urineurea nitrogen to plasma urea nitrogen ratio, a plasma BUN to creatnineratio, a renal failure index calculated as urine sodium/(urinecreatinine/plasma creatinine), a serum or plasma neutrophil gelatinase(NGAL) concentration, a urine NGAL concentration, a serum or plasmacystatin C concentration, a serum or plasma cardiac troponinconcentration, a serum or plasma BNP concentration, a serum or plasmaNTproBNP concentration, and a serum or plasma proBNP concentration.Other measures of renal function which may be combined with one or morekidney injury marker assay result(s) are described hereinafter and inHarrison's Principles of Internal Medicine, 17^(th) Ed., McGraw Hill,New York, pages 1741-1830, and Current Medical Diagnosis & Treatment2008, 47^(th) Ed, McGraw Hill, New York, pages 785-815, each of whichare hereby incorporated by reference in their entirety.

When more than one marker is measured, the individual markers may bemeasured in samples obtained at the same time, or may be determined fromsamples obtained at different (e.g., an earlier or later) times. Theindividual markers may also be measured on the same or different bodyfluid samples. For example, one kidney injury marker may be measured ina serum or plasma sample and another kidney injury marker may bemeasured in a urine sample. In addition, assignment of a likelihood maycombine an individual kidney injury marker assay result with temporalchanges in one or more additional variables.

In various related aspects, the present invention also relates todevices and kits for performing the methods described herein. Suitablekits comprise reagents sufficient for performing an assay for at leastone of the described kidney injury markers, together with instructionsfor performing the described threshold comparisons.

In certain embodiments, reagents for performing such assays are providedin an assay device, and such assay devices may be included in such akit. Preferred reagents can comprise one or more solid phase antibodies,the solid phase antibody comprising antibody that detects the intendedbiomarker target(s) bound to a solid support. In the case of sandwichimmunoassays, such reagents can also include one or more detectablylabeled antibodies, the detectably labeled antibody comprising antibodythat detects the intended biomarker target(s) bound to a detectablelabel. Additional optional elements that may be provided as part of anassay device are described hereinafter.

Detectable labels may include molecules that are themselves detectable(e.g., fluorescent moieties, electrochemical labels, ecl(electrochemical luminescence) labels, metal chelates, colloidal metalparticles, etc.) as well as molecules that may be indirectly detected byproduction of a detectable reaction product (e.g., enzymes such ashorseradish peroxidase, alkaline phosphatase, etc.) or through the useof a specific binding molecule which itself may be detectable (e.g., alabeled antibody that binds to the second antibody, biotin, digoxigenin,maltose, oligohistidine, 2,4-dintrobenzene, phenylarsenate, ssDNA,dsDNA, etc.).

Generation of a signal from the signal development element can beperformed using various optical, acoustical, and electrochemical methodswell known in the art. Examples of detection modes include fluorescence,radiochemical detection, reflectance, absorbance, amperometry,conductance, impedance, interferometry, ellipsometry, etc. In certain ofthese methods, the solid phase antibody is coupled to a transducer(e.g., a diffraction grating, electrochemical sensor, etc) forgeneration of a signal, while in others, a signal is generated by atransducer that is spatially separate from the solid phase antibody(e.g., a fluorometer that employs an excitation light source and anoptical detector). This list is not meant to be limiting. Antibody-basedbiosensors may also be employed to determine the presence or amount ofanalytes that optionally eliminate the need for a labeled molecule.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to methods and compositions for diagnosis,differential diagnosis, risk stratification, monitoring, classifying anddetermination of treatment regimens in subjects suffering or at risk ofsuffering from injury to renal function, reduced renal function and/oracute renal failure through measurement of one or more kidney injurymarkers. In various embodiments, a measured concentration of one or moremarkers selected from the group consisting of cytochrome c andinsulin-like growth factor IA, or one or more markers related thereto,are correlated to the renal status of the subject.

For purposes of this document, the following definitions apply:

As used herein, an “injury to renal function” is an abrupt (within 14days, preferably within 7 days, more preferably within 72 hours, andstill more preferably within 48 hours) measurable reduction in a measureof renal function. Such an injury may be identified, for example, by adecrease in glomerular filtration rate or estimated GFR, a reduction inurine output, an increase in serum creatinine, an increase in serumcystatin C, a requirement for renal replacement therapy, etc.“Improvement in Renal Function” is an abrupt (within 14 days, preferablywithin 7 days, more preferably within 72 hours, and still morepreferably within 48 hours) measurable increase in a measure of renalfunction. Preferred methods for measuring and/or estimating GFR aredescribed hereinafter.As used herein, “reduced renal function” is an abrupt (within 14 days,preferably within 7 days, more preferably within 72 hours, and stillmore preferably within 48 hours) reduction in kidney function identifiedby an absolute increase in serum creatinine of greater than or equal to0.1 mg/dL (≧8.8 μmol/L), a percentage increase in serum creatinine ofgreater than or equal to 20% (1.2-fold from baseline), or a reduction inurine output (documented oliguria of less than 0.5 ml/kg per hour).As used herein, “acute renal failure” or “ARF” is an abrupt (within 14days, preferably within 7 days, more preferably within 72 hours, andstill more preferably within 48 hours) reduction in kidney functionidentified by an absolute increase in serum creatinine of greater thanor equal to 0.3 mg/dl (≧26.4 μmol/l), a percentage increase in serumcreatinine of greater than or equal to 50% (1.5-fold from baseline), ora reduction in urine output (documented oliguria of less than 0.5 ml/kgper hour for at least 6 hours). This term is synonymous with “acutekidney injury” or “AKI.”

In this regard, the skilled artisan will understand that the signalsobtained from an immunoassay are a direct result of complexes formedbetween one or more antibodies and the target biomolecule (i.e., theanalyte) and polypeptides containing the necessary epitope(s) to whichthe antibodies bind. While such assays may detect the full lengthbiomarker and the assay result be expressed as a concentration of abiomarker of interest, the signal from the assay is actually a result ofall such “immunoreactive” polypeptides present in the sample. Expressionof biomarkers may also be determined by means other than immunoassays,including protein measurements (such as dot blots, western blots,chromatographic methods, mass spectrometry, etc.) and nucleic acidmeasurements (mRNA quatitation). This list is not meant to be limiting.

As used herein, the term “cytochrome c” refers to one or morepolypeptides present in a biological sample that are derived from thecytochrome c precursor (Swiss-Prot P99999 (SEQ ID NO: 1)).

        10         20         30         40MGDVEKGKKI FIMKCSQCHT VEKGGKHKTG PNLHGLFGRK        50         60         70         80TGQAPGYSYT AANKNKGIIW GEDTLMEYLE NPKKYIPGTK         90        100MIFVGIKKKE ERADLIAYLK KATNE

The following domains have been identified in cytochrome c:

Residues Length Domain ID 1 1 initiator methionine 2-105 385 cytochromec

As used herein, the term “insulin-like growth factor IA” refers to oneor more polypeptides present in a biological sample that are derivedfrom the insulin-like growth factor IA precursor (Swiss-Prot P01343 (SEQID NO: 2)).

        10         20         30         40MGKISSLPTQ LFKCCFCDFL KVKMHTMSSS HLFYLALCLL        50         60         70         80TFTSSATAGP ETLCGAELVD ALQFVCGDRG FYFNKPTGYG        90        100        110        120SSSRRAPQTG IVDECCFRSC DLRRLEMYCA PLKPAKSARS       130        140        150 VRAQRHTDMP KTQKEVHLKN ASRGSAGNKN YRM

The following domains have been identified in insulin-like growth factorIA:

Residues Length Domain ID  1-21 21 signal sequence 22-48 27 pro-peptide 49-118 70 insulin-like growth factor IA 119-153 35 pro-peptide E

As used herein, the term “relating a signal to the presence or amount”of an analyte reflects this understanding. Assay signals are typicallyrelated to the presence or amount of an analyte through the use of astandard curve calculated using known concentrations of the analyte ofinterest. As the term is used herein, an assay is “configured to detect”an analyte if an assay can generate a detectable signal indicative ofthe presence or amount of a physiologically relevant concentration ofthe analyte. Because an antibody epitope is on the order of 8 aminoacids, an immunoassay configured to detect a marker of interest willalso detect polypeptides related to the marker sequence, so long asthose polypeptides contain the epitope(s) necessary to bind to theantibody or antibodies used in the assay. The term “related marker” asused herein with regard to a biomarker such as one of the kidney injurymarkers described herein refers to one or more fragments, variants,etc., of a particular marker or its biosynthetic parent that may bedetected as a surrogate for the marker itself or as independentbiomarkers. The term also refers to one or more polypeptides present ina biological sample that are derived from the biomarker precursorcomplexed to additional species, such as binding proteins, receptors,heparin, lipids, sugars, etc.

The term “positive going” marker as that term is used herein refer to amarker that is determined to be elevated in subjects suffering from adisease or condition, relative to subjects not suffering from thatdisease or condition. The term “negative going” marker as that term isused herein refer to a marker that is determined to be reduced insubjects suffering from a disease or condition, relative to subjects notsuffering from that disease or condition.

The term “subject” as used herein refers to a human or non-humanorganism. Thus, the methods and compositions described herein areapplicable to both human and veterinary disease. Further, while asubject is preferably a living organism, the invention described hereinmay be used in post-mortem analysis as well. Preferred subjects arehumans, and most preferably “patients,” which as used herein refers toliving humans that are receiving medical care for a disease orcondition. This includes persons with no defined illness who are beinginvestigated for signs of pathology.

Preferably, an analyte is measured in a sample. Such a sample may beobtained from a subject, or may be obtained from biological materialsintended to be provided to the subject. For example, a sample may beobtained from a kidney being evaluated for possible transplantation intoa subject, and an analyte measurement used to evaluate the kidney forpreexisting damage. Preferred samples are body fluid samples.

The term “body fluid sample” as used herein refers to a sample of bodilyfluid obtained for the purpose of diagnosis, prognosis, classificationor evaluation of a subject of interest, such as a patient or transplantdonor. In certain embodiments, such a sample may be obtained for thepurpose of determining the outcome of an ongoing condition or the effectof a treatment regimen on a condition. Preferred body fluid samplesinclude blood, serum, plasma, cerebrospinal fluid, urine, saliva,sputum, and pleural effusions. In addition, one of skill in the artwould realize that certain body fluid samples would be more readilyanalyzed following a fractionation or purification procedure, forexample, separation of whole blood into serum or plasma components.

The term “diagnosis” as used herein refers to methods by which theskilled artisan can estimate and/or determine the probability (“alikelihood”) of whether or not a patient is suffering from a givendisease or condition. In the case of the present invention, “diagnosis”includes using the results of an assay, most preferably an immunoassay,for a kidney injury marker of the present invention, optionally togetherwith other clinical characteristics, to arrive at a diagnosis (that is,the occurrence or nonoccurrence) of an acute renal injury or ARF for thesubject from which a sample was obtained and assayed. That such adiagnosis is “determined” is not meant to imply that the diagnosis is100% accurate. Many biomarkers are indicative of multiple conditions.The skilled clinician does not use biomarker results in an informationalvacuum, but rather test results are used together with other clinicalindicia to arrive at a diagnosis. Thus, a measured biomarker level onone side of a predetermined diagnostic threshold indicates a greaterlikelihood of the occurrence of disease in the subject relative to ameasured level on the other side of the predetermined diagnosticthreshold.

Similarly, a prognostic risk signals a probability (“a likelihood”) thata given course or outcome will occur. A level or a change in level of aprognostic indicator, which in turn is associated with an increasedprobability of morbidity (e.g., worsening renal function, future ARF, ordeath) is referred to as being “indicative of an increased likelihood”of an adverse outcome in a patient.

Marker Assays

In general, immunoassays involve contacting a sample containing orsuspected of containing a biomarker of interest with at least oneantibody that specifically binds to the biomarker. A signal is thengenerated indicative of the presence or amount of complexes formed bythe binding of polypeptides in the sample to the antibody. The signal isthen related to the presence or amount of the biomarker in the sample.Numerous methods and devices are well known to the skilled artisan forthe detection and analysis of biomarkers. See, e.g., U.S. Pat. Nos.6,143,576; 6,113,855; 6,019,944; 5,985,579; 5,947,124; 5,939,272;5,922,615; 5,885,527; 5,851,776; 5,824,799; 5,679,526; 5,525,524; and5,480,792, and The Immunoassay Handbook, David Wild, ed. Stockton Press,New York, 1994, each of which is hereby incorporated by reference in itsentirety, including all tables, figures and claims.

The assay devices and methods known in the art can utilize labeledmolecules in various sandwich, competitive, or non-competitive assayformats, to generate a signal that is related to the presence or amountof the biomarker of interest. Suitable assay formats also includechromatographic, mass spectrographic, and protein “blotting” methods.Additionally, certain methods and devices, such as biosensors andoptical immunoassays, may be employed to determine the presence oramount of analytes without the need for a labeled molecule. See, e.g.,U.S. Pat. Nos. 5,631,171; and 5,955,377, each of which is herebyincorporated by reference in its entirety, including all tables, figuresand claims. One skilled in the art also recognizes that roboticinstrumentation including but not limited to Beckman ACCESS®, AbbottAXSYM®, Roche ELECSYS®, Dade Behring STRATUS® systems are among theimmunoassay analyzers that are capable of performing immunoassays. Butany suitable immunoassay may be utilized, for example, enzyme-linkedimmunoassays (ELISA), radioimmunoassays (RIAs), competitive bindingassays, and the like.

Antibodies or other polypeptides may be immobilized onto a variety ofsolid supports for use in assays. Solid phases that may be used toimmobilize specific binding members include include those developedand/or used as solid phases in solid phase binding assays. Examples ofsuitable solid phases include membrane filters, cellulose-based papers,beads (including polymeric, latex and paramagnetic particles), glass,silicon wafers, microparticles, nanoparticles, TentaGels, AgroGels, PEGAgels, SPOCC gels, and multiple-well plates. An assay strip could beprepared by coating the antibody or a plurality of antibodies in anarray on solid support. This strip could then be dipped into the testsample and then processed quickly through washes and detection steps togenerate a measurable signal, such as a colored spot. Antibodies orother polypeptides may be bound to specific zones of assay deviceseither by conjugating directly to an assay device surface, or byindirect binding. In an example of the later case, antibodies or otherpolypeptides may be immobilized on particles or other solid supports,and that solid support immobilized to the device surface.

Biological assays require methods for detection, and one of the mostcommon methods for quantitation of results is to conjugate a detectablelabel to a protein or nucleic acid that has affinity for one of thecomponents in the biological system being studied. Detectable labels mayinclude molecules that are themselves detectable (e.g., fluorescentmoieties, electrochemical labels, metal chelates, etc.) as well asmolecules that may be indirectly detected by production of a detectablereaction product (e.g., enzymes such as horseradish peroxidase, alkalinephosphatase, etc.) or by a specific binding molecule which itself may bedetectable (e.g., biotin, digoxigenin, maltose, oligohistidine,2,4-dintrobenzene, phenylarsenate, ssDNA, dsDNA, etc.).

Preparation of Solid Phases and Detectable Label Conjugates OftenComprise the Use of chemical cross-linkers. Cross-linking reagentscontain at least two reactive groups, and are divided generally intohomofunctional cross-linkers (containing identical reactive groups) andheterofunctional cross-linkers (containing non-identical reactivegroups). Homobifunctional cross-linkers that couple through amines,sulfhydryls or react non-specifically are available from many commercialsources. Maleimides, alkyl and aryl halides, alpha-haloacyls and pyridyldisulfides are thiol reactive groups. Maleimides, alkyl and arylhalides, and alpha-haloacyls react with sulfhydryls to form thiol etherbonds, while pyridyl disulfides react with sulfhydryls to produce mixeddisulfides. The pyridyl disulfide product is cleavable. Imidoesters arealso very useful for protein-protein cross-links. A variety ofheterobifunctional cross-linkers, each combining different attributesfor successful conjugation, are commercially available.

In certain aspects, the present invention provides kits for the analysisof the described kidney injury markers. The kit comprises reagents forthe analysis of at least one test sample which comprise at least oneantibody that a kidney injury marker. The kit can also include devicesand instructions for performing one or more of the diagnostic and/orprognostic correlations described herein. Preferred kits will comprisean antibody pair for performing a sandwich assay, or a labeled speciesfor performing a competitive assay, for the analyte. Preferably, anantibody pair comprises a first antibody conjugated to a solid phase anda second antibody conjugated to a detectable label, wherein each of thefirst and second antibodies that bind a kidney injury marker. Mostpreferably each of the antibodies are monoclonal antibodies. Theinstructions for use of the kit and performing the correlations can bein the form of labeling, which refers to any written or recordedmaterial that is attached to, or otherwise accompanies a kit at any timeduring its manufacture, transport, sale or use. For example, the termlabeling encompasses advertising leaflets and brochures, packagingmaterials, instructions, audio or video cassettes, computer discs, aswell as writing imprinted directly on kits.

Antibodies

The term “antibody” as used herein refers to a peptide or polypeptidederived from, modeled after or substantially encoded by animmunoglobulin gene or immunoglobulin genes, or fragments thereof,capable of specifically binding an antigen or epitope. See, e.g.Fundamental Immunology, 3rd Edition, W. E. Paul, ed., Raven Press, N.Y.(1993); Wilson (1994; J. Immunol. Methods 175:267-273; Yarmush (1992) J.Biochem. Biophys. Methods 25:85-97. The term antibody includesantigen-binding portions, i.e., “antigen binding sites,” (e.g.,fragments, subsequences, complementarity determining regions (CDRs))that retain capacity to bind antigen, including (i) a Fab fragment, amonovalent fragment consisting of the VL, VH, CL and CH1 domains; (ii) aF(ab′)2 fragment, a bivalent fragment comprising two Fab fragmentslinked by a disulfide bridge at the hinge region; (iii) a Fd fragmentconsisting of the VH and CH1 domains; (iv) a Fv fragment consisting ofthe VL and VH domains of a single arm of an antibody, (v) a dAb fragment(Ward et al., (1989) Nature 341:544-546), which consists of a VH domain;and (vi) an isolated complementarity determining region (CDR). Singlechain antibodies are also included by reference in the term “antibody.”

Antibodies used in the immunoassays described herein preferablyspecifically bind to a kidney injury marker of the present invention.The term “specifically binds” is not intended to indicate that anantibody binds exclusively to its intended target since, as noted above,an antibody binds to any polypeptide displaying the epitope(s) to whichthe antibody binds. Rather, an antibody “specifically binds” if itsaffinity for its intended target is about 5-fold greater when comparedto its affinity for a non-target molecule which does not display theappropriate epitope(s). Preferably the affinity of the antibody will beat least about 5 fold, preferably 10 fold, more preferably 25-fold, evenmore preferably 50-fold, and most preferably 100-fold or more, greaterfor a target molecule than its affinity for a non-target molecule. Inpreferred embodiments, Preferred antibodies bind with affinities of atleast about 10⁷ M⁻¹, and preferably between about 10⁸ M⁻¹ to about 10⁹M⁻¹, about 10⁹ M⁻¹ to about 10¹⁰ M⁻¹, or about 10¹⁰ M⁻¹ to about 10¹²M⁻¹.

Affinity is calculated as K_(d)=k_(off)/k_(on) (k_(off) is thedissociation rate constant, K_(on) is the association rate constant andK_(d) is the equilibrium constant). Affinity can be determined atequilibrium by measuring the fraction bound (r) of labeled ligand atvarious concentrations (c). The data are graphed using the Scatchardequation: r/c=K(n−r): where r=moles of bound ligand/mole of receptor atequilibrium; c=free ligand concentration at equilibrium; K=equilibriumassociation constant; and n=number of ligand binding sites per receptormolecule. By graphical analysis, r/c is plotted on the Y-axis versus ron the X-axis, thus producing a Scatchard plot. Antibody affinitymeasurement by Scatchard analysis is well known in the art. See, e.g.,van Erp et al., J. Immunoassay 12: 425-43, 1991; Nelson and Griswold,Comput. Methods Programs Biomed. 27: 65-8, 1988.

The term “epitope” refers to an antigenic determinant capable ofspecific binding to an antibody. Epitopes usually consist of ichemicallyactive surface groupings of molecules such as amino acids or sugar sidechains and usually have specific three dimensional structuralcharacteristics, as well as specific charge characteristics.Conformational and nonconformational epitopes are distinguished in thatthe binding to the former but not the latter is lost in the presence ofdenaturing solvents.

Numerous publications discuss the use of phage display technology toproduce and screen libraries of polypeptides for binding to a selectedanalyte. See, e.g, Cwirla et al., Proc. Natl. Acad. Sci. USA 87,6378-82, 1990; Devlin et al., Science 249, 404-6, 1990, Scott and Smith,Science 249, 386-88, 1990; and Ladner et al., U.S. Pat. No. 5,571,698. Abasic concept of phage display methods is the establishment of aphysical association between DNA encoding a polypeptide to be screenedand the polypeptide. This physical association is provided by the phageparticle, which displays a polypeptide as part of a capsid enclosing thephage genome which encodes the polypeptide. The establishment of aphysical association between polypeptides and their genetic materialallows simultaneous mass screening of very large numbers of phagebearing different polypeptides. Phage displaying a polypeptide withaffinity to a target bind to the target and these phage are enriched byaffinity screening to the target. The identity of polypeptides displayedfrom these phage can be determined from their respective genomes. Usingthese methods a polypeptide identified as having a binding affinity fora desired target can then be synthesized in bulk by conventional means.See, e.g., U.S. Pat. No. 6,057,098, which is hereby incorporated in itsentirety, including all tables, figures, and claims.

The antibodies that are generated by these methods may then be selectedby first screening for affinity and specificity with the purifiedpolypeptide of interest and, if required, comparing the results to theaffinity and specificity of the antibodies with polypeptides that aredesired to be excluded from binding. The screening procedure can involveimmobilization of the purified polypeptides in separate wells ofmicrotiter plates. The solution containing a potential antibody orgroups of antibodies is then placed into the respective microtiter wellsand incubated for about 30 min to 2 h. The microtiter wells are thenwashed and a labeled secondary antibody (for example, an anti-mouseantibody conjugated to alkaline phosphatase if the raised antibodies aremouse antibodies) is added to the wells and incubated for about 30 minand then washed. Substrate is added to the wells and a color reactionwill appear where antibody to the immobilized polypeptide(s) arepresent.

The antibodies so identified may then be further analyzed for affinityand specificity in the assay design selected. In the development ofimmunoassays for a target protein, the purified target protein acts as astandard with which to judge the sensitivity and specificity of theimmunoassay using the antibodies that have been selected. Because thebinding affinity of various antibodies may differ; certain antibodypairs (e.g., in sandwich assays) may interfere with one anothersterically, etc., assay performance of an antibody may be a moreimportant measure than absolute affinity and specificity of an antibody.

Assay Correlations

The term “correlating” as used herein in reference to the use ofbiomarkers refers to comparing the presence or amount of thebiomarker(s) in a patient to its presence or amount in persons known tosuffer from, or known to be at risk of, a given condition; or in personsknown to be free of a given condition. Often, this takes the form ofcomparing an assay result in the form of a biomarker concentration to apredetermined threshold selected to be indicative of the occurrence ornonoccurrence of a disease or the likelihood of some future outcome.

Selecting a diagnostic threshold involves, among other things,consideration of the probability of disease, distribution of true andfalse diagnoses at different test thresholds, and estimates of theconsequences of treatment (or a failure to treat) based on thediagnosis. For example, when considering administering a specifictherapy which is highly efficacious and has a low level of risk, fewtests are needed because clinicians can accept substantial diagnosticuncertainty. On the other hand, in situations where treatment optionsare less effective and more risky, clinicians often need a higher degreeof diagnostic certainty. Thus, cost/benefit analysis is involved inselecting a diagnostic threshold.

Suitable thresholds may be determined in a variety of ways. For example,one recommended diagnostic threshold for the diagnosis of acutemyocardial infarction using cardiac troponin is the 97.5^(th) percentileof the concentration seen in a normal population. Another method may beto look at serial samples from the same patient, where a prior“baseline” result is used to monitor for temporal changes in a biomarkerlevel.

Population studies may also be used to select a decision threshold.Reciever Operating Characteristic (“ROC”) arose from the field of signaldectection therory developed during World War II for the analysis ofradar images, and ROC analysis is often used to select a threshold ableto best distinguish a “diseased” subpopulation from a “nondiseased”subpopulation. A false positive in this case occurs when the persontests positive, but actually does not have the disease. A falsenegative, on the other hand, occurs when the person tests negative,suggesting they are healthy, when they actually do have the disease. Todraw a ROC curve, the true positive rate (TPR) and false positive rate(FPR) are determined as the decision threshold is varied continuously.Since TPR is equivalent with sensitivity and FPR is equal to1—specificity, the ROC graph is sometimes called the sensitivity vs(1—specificity) plot. A perfect test will have an area under the ROCcurve of 1.0; a random test will have an area of 0.5. A threshold isselected to provide an acceptable level of specificity and sensitivity.

In this context, “diseased” is meant to refer to a population having onecharacteristic (the presence of a disease or condition or the occurrenceof some outcome) and “nondiseased” is meant to refer to a populationlacking the characteristic. While a single decision threshold is thesimplest application of such a method, multiple decision thresholds maybe used. For example, below a first threshold, the absence of diseasemay be assigned with relatively high confidence, and above a secondthreshold the presence of disease may also be assigned with relativelyhigh confidence. Between the two thresholds may be consideredindeterminate. This is meant to be exemplary in nature only.

In addition to threshold comparisons, other methods for correlatingassay results to a patient classification (occurrence or nonoccurrenceof disease, likelihood of an outcome, etc.) include decision trees, rulesets, Bayesian methods, and neural network methods. These methods canproduce probability values representing the degree to which a subjectbelongs to one classification out of a plurality of classifications.

Measures of test accuracy may be obtained as described in Fischer etal., Intensive Care Med. 29: 1043-51, 2003, and used to determine theeffectiveness of a given biomarker. These measures include sensitivityand specificity, predictive values, likelihood ratios, diagnostic oddsratios, and ROC curve areas. The area under the curve (“AUC”) of a ROCplot is equal to the probability that a classifier will rank a randomlychosen positive instance higher than a randomly chosen negative one. Thearea under the ROC curve may be thought of as equivalent to theMann-Whitney U test, which tests for the median difference betweenscores obtained in the two groups considered if the groups are ofcontinuous data, or to the Wilcoxon test of ranks.

As discussed above, suitable tests may exhibit one or more of thefollowing results on these various measures: a specificity of greaterthan 0.5, preferably at least 0.6, more preferably at least 0.7, stillmore preferably at least 0.8, even more preferably at least 0.9 and mostpreferably at least 0.95, with a corresponding sensitivity greater than0.2, preferably greater than 0.3, more preferably greater than 0.4,still more preferably at least 0.5, even more preferably 0.6, yet morepreferably greater than 0.7, still more preferably greater than 0.8,more preferably greater than 0.9, and most preferably greater than 0.95;a sensitivity of greater than 0.5, preferably at least 0.6, morepreferably at least 0.7, still more preferably at least 0.8, even morepreferably at least 0.9 and most preferably at least 0.95, with acorresponding specificity greater than 0.2, preferably greater than 0.3,more preferably greater than 0.4, still more preferably at least 0.5,even more preferably 0.6, yet more preferably greater than 0.7, stillmore preferably greater than 0.8, more preferably greater than 0.9, andmost preferably greater than 0.95; at least 75% sensitivity, combinedwith at least 75% specificity; a ROC curve area of greater than 0.5,preferably at least 0.6, more preferably 0.7, still more preferably atleast 0.8, even more preferably at least 0.9, and most preferably atleast 0.95; an odds ratio different from 1, preferably at least about 2or more or about 0.5 or less, more preferably at least about 3 or moreor about 0.33 or less, still more preferably at least about 4 or more orabout 0.25 or less, even more preferably at least about 5 or more orabout 0.2 or less, and most preferably at least about 10 or more orabout 0.1 or less; a positive likelihood ratio (calculated assensitivity/(1-specificity)) of greater than 1, at least 2, morepreferably at least 3, still more preferably at least 5, and mostpreferably at least 10; and or a negative likelihood ratio (calculatedas (1-sensitivity)/specificity) of less than 1, less than or equal to0.5, more preferably less than or equal to 0.3, and most preferably lessthan or equal to 0.1

Additional clinical indicia may be combined with the kidney injurymarker assay result(s) of the present invention. These include otherbiomarkers related to renal status. Examples include the following,which recite the common biomarker name, followed by the Swiss-Prot entrynumber for that biomarker or its parent: Actin (P68133); Adenosinedeaminase binding protein (DPP4, P27487); Alpha-1-acid glycoprotein 1(P0763); Alpha-1-microglobulin (P02760); Albumin (P02768);Angiotensinogenase (Renin, P00797); Annexin A2 (P07355);Beta-glucuronidase (P08236); B-2-microglobulin (P61679);Beta-galactosidase (P16278); BMP-7 (P18075); Brain natriuretic peptide(proBNP, BNP-32, NTproBNP; P16860); Calcium-binding protein Beta(S100-beta, P04271); Carbonic anhydrase (Q16790); Casein Kinase 2(P68400); Cathepsin B (P07858); Ceruloplasmin (P00450); Clusterin(P10909); Complement C3 (P01024); Cysteine-rich protein (CYR61, 000622);Cytochrome C(P99999); Epidermal growth factor (EGF, P01133);Endothelin-1 (P05305); Exosomal Fetuin-A (P02765); Fatty acid-bindingprotein, heart (FABP3, P05413); Fatty acid-binding protein, liver(P07148); Ferritin (light chain, P02793; heavy chain P02794);Fructose-1,6-biphosphatase (P09467); GRO-alpha (CXCL1, (P09341); GrowthHormone (P01241); Hepatocyte growth factor (P14210); Insulin-like growthfactor I (P01343); Immunoglobulin G; Immunoglobulin Light Chains (Kappaand Lambda); Interferon gamma (P01308); Lysozyme (P61626);Interleukin-1alpha (P01583); Interleukin-2 (P60568); Interleukin-4(P60568); Interleukin-9 (P15248); Interleukin-12p40 (P29460);Interleukin-13 (P35225); Interleukin-16 (Q14005); Ll cell adhesionmolecule (P32004); Lactate dehydrogenase (P00338); LeucineAminopeptidase (P28838); Meprin A-alpha subunit (Q16819); Meprin A-betasubunit (Q16820); Midkine (P21741); MIP2-alpha (CXCL2, P19875); MMP-2(P08253); MMP-9 (P14780); Netrin-1 (O95631); Neutral endopeptidase(P08473); Osteopontin (P10451); Renal papillary antigen 1 (RPA1); Renalpapillary antigen 2 (RPA2); Retinol binding protein (P09455);Ribonuclease; S100 calcium-binding protein A6 (P06703); Serum Amyloid PComponent (P02743); Sodium/Hydrogen exchanger isoform (NHE3, P48764);Spermidine/spermine N1-acetyltransferase (P21673); TGF-Beta1 (P01137);Transferrin (P02787); Trefoil factor 3 (TFF3, Q07654); Toll-Like protein4 (O00206); Total protein; Tubulointerstitial nephritis antigen(Q9UJW2); Uromodulin (Tamm-Horsfall protein, P07911).

For purposes of risk stratification, Adiponectin (Q15848); Alkalinephosphatase (P05186); Aminopeptidase N(P15144); CalbindinD28k (P05937);Cystatin C(P01034); 8 subunit of FIFO ATPase (P03928);Gamma-glutamyltransferase (P19440); GSTa(alpha-glutathione-S-transferase, P08263); GSTpi(Glutathione-S-transferase P; GST class-pi; P09211); IGFBP-1 (P08833);IGFBP-2 (P18065); IGFBP-6 (P24592); Integral membrane protein 1 (Itml,P46977); Interleukin-6 (P05231); Interleukin-8 (P10145); Interleukin-18(Q14116); IP-10 (10 kDa interferon-gamma-induced protein, P02778); IRPR(IFRD1, 000458); Isovaleryl-CoA dehydrogenase (IVD, P26440);I-TAC/CXCL11 (O14625); Keratin 19 (P08727); Kim-1 (Hepatitis A viruscellular receptor 1, O43656); L-arginine:glycine amidinotransferase(P50440); Leptin (P41159); Lipocalin2 (NGAL, P80188); MCP-1 (P13500);MIG (Gamma-interferon-induced monokine Q07325); MIP-1α (P10147); MIP-3a(P78556); MIP-1beta (P13236); MIP-1d (Q16663); NAG(N-acetyl-beta-D-glucosaminidase, P54802); Organic ion transporter(OCT2, O15244); Osteoprotegerin (O14788); P8 protein (O60356);Plasminogen activator inhibitor 1 (PAI-1, P05121); ProANP(1-98)(P01160); Protein phosphatase 1-beta (PPI-beta, P62140); Rab GDI-beta(P50395); Renal kallikrein (Q86U61); RT1.B-1 (alpha) chain of theintegral membrane protein (Q5Y7A8); Soluble tumor necrosis factorreceptor superfamily member 1A (sTNFR-I, P19438); Soluble tumor necrosisfactor receptor superfamily member 1B (sTNFR-II, P20333); Tissueinhibitor of metalloproteinases 3 (TIMP-3, P35625); uPAR (Q03405) may becombined with the kidney injury marker assay result(s) of the presentinvention.

Other clinical indicia which may be combined with the kidney injurymarker assay result(s) of the present invention includes demographicinformation (e.g., weight, sex, age, race), medical history (e.g.,family history, type of surgery, pre-existing disease such as aneurism,congestive heart failure, preeclampsia, eclampsia, diabetes mellitus,hypertension, coronary artery disease, proteinuria, renal insufficiency,or sepsis, type of toxin exposure such as NSAIDs, cyclosporines,tacrolimus, aminoglycosides, foscarnet, ethylene glycol, hemoglobin,myoglobin, ifosfamide, heavy metals, methotrexate, radiopaque contrastagents, or streptozotocin), clinical variables (e.g., blood pressure,temperature, respiration rate), risk scores (APACHE score, PREDICTscore, TIMI Risk Score for UA/NSTEMI, Framingham Risk Score), a urinetotal protein measurement, a glomerular filtration rate, an estimatedglomerular filtration rate, a urine production rate, a serum or plasmacreatinine concentration, a renal papillary antigen 1 (RPA1)measurement; a renal papillary antigen 2 (RPA2) measurement; a urinecreatinine concentration, a fractional excretion of sodium, a urinesodium concentration, a urine creatinine to serum or plasma creatinineratio, a urine specific gravity, a urine osmolality, a urine ureanitrogen to plasma urea nitrogen ratio, a plasma BUN to creatnine ratio,and/or a renal failure index calculated as urine sodium/(urinecreatinine/plasma creatinine). Other measures of renal function whichmay be combined with the kidney injury marker assay result(s) aredescribed hereinafter and in Harrison's Principles of Internal Medicine,17^(th) Ed., McGraw Hill, New York, pages 1741-1830, and Current MedicalDiagnosis & Treatment 2008, 47^(th) Ed, McGraw Hill, New York, pages785-815, each of which are hereby incorporated by reference in theirentirety.

Combining assay results/clinical indicia in this manner can comprise theuse of multivariate logistical regression, loglinear modeling, neuralnetwork analysis, n-of-m analysis, decision tree analysis, etc. Thislist is not meant to be limiting.

Diagnosis of Acute Renal Failure

As noted above, the terms “acute renal (or kidney) injury” and “acuterenal (or kidney) failure” as used herein are defined in part in termsof changes in serum creatinine from a baseline value. Most definitionsof ARF have common elements, including the use of serum creatinine and,often, urine output. Patients may present with renal dysfunction withoutan available baseline measure of renal function for use in thiscomparison. In such an event, one may estimate a baseline serumcreatinine value by assuming the patient initially had a normal GFR.Glomerular filtration rate (GFR) is the volume of fluid filtered fromthe renal (kidney) glomerular capillaries into the Bowman's capsule perunit time. Glomerular filtration rate (GFR) can be calculated bymeasuring any chemical that has a steady level in the blood, and isfreely filtered but neither reabsorbed nor secreted by the kidneys. GFRis typically expressed in units of ml/min:

${GFR} = \frac{{Urine}\mspace{14mu} {Concentration} \times {Urine}\mspace{14mu} {Flow}}{{Plasma}\mspace{14mu} {Concentration}}$

By normalizing the GFR to the body surface area, a GFR of approximately75-100 ml/min per 1.73 m² can be assumed. The rate therefore measured isthe quantity of the substance in the urine that originated from acalculable volume of blood.

There are several different techniques used to calculate or estimate theglomerular filtration rate (GFR or eGFR). In clinical practice, however,creatinine clearance is used to measure GFR. Creatinine is producednaturally by the body (creatinine is a metabolite of creatine, which isfound in muscle). It is freely filtered by the glomerulus, but alsoactively secreted by the renal tubules in very small amounts such thatcreatinine clearance overestimates actual GFR by 10-20%. This margin oferror is acceptable considering the ease with which creatinine clearanceis measured.

Creatinine clearance (CCr) can be calculated if values for creatinine'surine concentration (U_(Cr)), urine flow rate (V), and creatinine'splasma concentration (P_(Cr)) are known. Since the product of urineconcentration and urine flow rate yields creatinine's excretion rate,creatinine clearance is also said to be its excretion rate (U_(Cr)×V)divided by its plasma concentration. This is commonly representedmathematically as:

$C_{Cr} = \frac{U_{Cr} \times V}{P_{Cr}}$

Commonly a 24 hour urine collection is undertaken, from empty-bladderone morning to the contents of the bladder the following morning, with acomparative blood test then taken:

$C_{Cr} = \frac{U_{Cr} \times 24\text{-}{hour}\mspace{14mu} {volume}}{P_{Cr} \times 24 \times 60\mspace{14mu} {mins}}$

To allow comparison of results between people of different sizes, theCCr is often corrected for the body surface area (BSA) and expressedcompared to the average sized man as ml/min/1.73 m2. While most adultshave a BSA that approaches 1.7 (1.6-1.9), extremely obese or slimpatients should have their CCr corrected for their actual BSA:

$C_{{Cr}\text{-}{corrected}} = \frac{C_{Cr} \times 1.73}{BSA}$

The accuracy of a creatinine clearance measurement (even when collectionis complete) is limited because as glomerular filtration rate (GFR)falls creatinine secretion is increased, and thus the rise in serumcreatinine is less. Thus, creatinine excretion is much greater than thefiltered load, resulting in a potentially large overestimation of theGFR (as much as a twofold difference). However, for clinical purposes itis important to determine whether renal function is stable or gettingworse or better. This is often determined by monitoring serum creatininealone. Like creatinine clearance, the serum creatinine will not be anaccurate reflection of GFR in the non-steady-state condition of ARF.Nonetheless, the degree to which serum creatinine changes from baselinewill reflect the change in GFR. Serum creatinine is readily and easilymeasured and it is specific for renal function.

For purposes of determining urine output on a Urine output on a mL/kg/hrbasis, hourly urine collection and measurement is adequate. In the casewhere, for example, only a cumulative 24-h output was available and nopatient weights are provided, minor modifications of the RIFLE urineoutput criteria have been described. For example, Bagshaw et al.,Nephrol. Dial. Transplant. 23: 1203-1210, 2008, assumes an averagepatient weight of 70 kg, and patients are assigned a RIFLEclassification based on the following: <35 mL/h (Risk), <21 mL/h(Injury) or <4 mL/h (Failure).

Selecting a Treatment Regimen

Once a diagnosis is obtained, the clinician can readily select atreatment regimen that is compatible with the diagnosis, such asinitiating renal replacement therapy, withdrawing delivery of compoundsthat are known to be damaging to the kidney, kidney transplantation,delaying or avoiding procedures that are known to be damaging to thekidney, modifying diuretic administration, initiating goal directedtherapy, etc. The skilled artisan is aware of appropriate treatments fornumerous diseases discussed in relation to the methods of diagnosisdescribed herein. See, e.g., Merck Manual of Diagnosis and Therapy, 17thEd. Merck Research Laboratories, Whitehouse Station, N.J., 1999. Inaddition, since the methods and compositions described herein provideprognostic information, the markers of the present invention may be usedto monitor a course of treatment. For example, improved or worsenedprognostic state may indicate that a particular treatment is or is notefficacious.

One skilled in the art readily appreciates that the present invention iswell adapted to carry out the objects and obtain the ends and advantagesmentioned, as well as those inherent therein. The examples providedherein are representative of preferred embodiments, are exemplary, andare not intended as limitations on the scope of the invention.

Example 1 Contrast-Induced Nephropathy Sample Collection

The objective of this sample collection study is to collect samples ofplasma and urine and clinical data from patients before and afterreceiving intravascular contrast media. Approximately 250 adultsundergoing radiographic/angiographic procedures involving intravascularadministration of iodinated contrast media are enrolled. To be enrolledin the study, each patient must meet all of the following inclusioncriteria and none of the following exclusion criteria:

Inclusion Criteria

males and females 18 years of age or older;undergoing a radiographic/angiographic procedure (such as a CT scan orcoronary intervention) involving the intravascular administration ofcontrast media;expected to be hospitalized for at least 48 hours after contrastadministration.able and willing to provide written informed consent for studyparticipation and to comply with all study procedures.

Exclusion Criteria

renal transplant recipients;acutely worsening renal function prior to the contrast procedure;already receiving dialysis (either acute or chronic) or in imminent needof dialysis at enrollment;expected to undergo a major surgical procedure (such as involvingcardiopulmonary bypass) or an additional imaging procedure with contrastmedia with significant risk for further renal insult within the 48 hrsfollowing contrast administration;participation in an interventional clinical study with an experimentaltherapy within the previous 30 days;known infection with human immunodeficiency virus (HW) or a hepatitisvirus.

Immediately prior to the first contrast administration (and after anypre-procedure hydration), an EDTA anti-coagulated blood sample (10 mL)and a urine sample (10 mL) are collected from each patient. Blood andurine samples are then collected at 4 (±0.5), 8 (±1), 24 (±2) 48 (±2),and 72 (±2) hrs following the last administration of contrast mediaduring the index contrast procedure. Blood is collected via directvenipuncture or via other available venous access, such as an existingfemoral sheath, central venous line, peripheral intravenous line orhep-lock. These study blood samples are processed to plasma at theclinical site, frozen and shipped to Astute Medical, Inc., San Diego,Calif. The study urine samples are frozen and shipped to Astute Medical,Inc.

Serum creatinine is assessed at the site immediately prior to the firstcontrast administration (after any pre-procedure hydration) and at 4(±0.5), 8 (±1), 24 (±2) and 48 (±2)), and 72 (±2) hours following thelast administration of contrast (ideally at the same time as the studysamples are obtained). In addition, each patient's status is evaluatedthrough day 30 with regard to additional serum and urine creatininemeasurements, a need for dialysis, hospitalization status, and adverseclinical outcomes (including mortality).

Prior to contrast administration, each patient is assigned a risk basedon the following assessment: systolic blood pressure <80 mm Hg=5 points;intra-arterial balloon pump=5 points; congestive heart failure (ClassIII-IV or history of pulmonary edema)=5 points; age >75 yrs=4 points;hematocrit level <39% for men, <35% for women=3 points; diabetes=3points; contrast media volume=1 point for each 100 mL; serum creatininelevel >1.5 g/dL=4 points OR estimated GFR 40-60 mL/min/1.73 m²=2 points,20-40 mL/min/1.73 m²=4 points, <20 mL/min/1.73 m²=6 points. The risksassigned are as follows: risk for CIN and dialysis: 5 or less totalpoints=risk of CIN—7.5%, risk of dialysis—0.04%; 6-10 total points=riskof CIN—14%, risk of dialysis—0.12%; 11-16 total points=risk ofCIN—26.1%, risk of dialysis—1.09%; >16 total points=risk of CIN—57.3%,risk of dialysis—12.8%.

Example 2 Cardiac Surgery Sample Collection

The objective of this sample collection study is to collect samples ofplasma and urine and clinical data from patients before and afterundergoing cardiovascular surgery, a procedure known to be potentiallydamaging to kidney function. Approximately 900 adults undergoing suchsurgery are enrolled. To be enrolled in the study, each patient mustmeet all of the following inclusion criteria and none of the followingexclusion criteria:

Inclusion Criteria

males and females 18 years of age or older;undergoing cardiovascular surgery;Toronto/Ottawa Predictive Risk Index for Renal Replacement risk score ofat least 2 (Wijeysundera et al., JAMA 297: 1801-9, 2007); andable and willing to provide written informed consent for studyparticipation and to comply with all study procedures.

Exclusion Criteria

known pregnancy;previous renal transplantation;acutely worsening renal function prior to enrollment (e.g., any categoryof RIFLE criteria);already receiving dialysis (either acute or chronic) or in imminent needof dialysis at enrollment;currently enrolled in another clinical study or expected to be enrolledin another clinical study within 7 days of cardiac surgery that involvesdrug infusion or a therapeutic intervention for AKI;known infection with human immunodeficiency virus (HIV) or a hepatitisvirus.

Within 3 hours prior to the first incision (and after any pre-procedurehydration), an EDTA anti-coagulated blood sample (10 mL), whole blood (3mL), and a urine sample (35 mL) are collected from each patient. Bloodand urine samples are then collected at 3 (±0.5), 6 (±0.5), 12 (±1), 24(±2) and 48 (±2) hrs following the procedure and then daily on days 3through 7 if the subject remains in the hospital. Blood is collected viadirect venipuncture or via other available venous access, such as anexisting femoral sheath, central venous line, peripheral intravenousline or hep-lock. These study blood samples are frozen and shipped toAstute Medical, Inc., San Diego, Calif. The study urine samples arefrozen and shipped to Astute Medical, Inc.

Example 3 Acutely Ill Subject Sample Collection

The objective of this study is to collect samples from acutely illpatients. Approximately 900 adults expected to be in the ICU for atleast 48 hours will be enrolled. To be enrolled in the study, eachpatient must meet all of the following inclusion criteria and none ofthe following exclusion criteria:

Inclusion Criteria

males and females 18 years of age or older;Study population 1: approximately 300 patients that have at least oneof:shock (SBP<90 mmHg and/or need for vasopressor support to maintainMAP>60 mmHg and/or documented drop in SBP of at least 40 mmHg); andsepsis;Study population 2: approximately 300 patients that have at least oneof:IV antibiotics ordered in computerized physician order entry (CPOE)within 24 hours of enrollment;contrast media exposure within 24 hours of enrollment;increased Intra-Abdominal Pressure with acute decompensated heartfailure; andsevere trauma as the primary reason for ICU admission and likely to behospitalized in the ICU for 48 hours after enrollment;Study population 3: approximately 300 patientsexpected to be hospitalized through acute care setting (ICU or ED) witha known risk factor for acute renal injury (e.g. sepsis,hypotension/shock (Shock=systolic BP<90 mmHg and/or the need forvasopressor support to maintain a MAP>60 mmHg and/or a documented dropin SBP>40 mmHg), major trauma, hemorrhage, or major surgery); and/orexpected to be hospitalized to the ICU for at least 24 hours afterenrollment.

Exclusion Criteria

known pregnancy;institutionalized individuals;previous renal transplantation;known acutely worsening renal function prior to enrollment (e.g., anycategory of RIFLE criteria);received dialysis (either acute or chronic) within 5 days prior toenrollment or in imminent need of dialysis at the time of enrollment;known infection with human immunodeficiency virus (HIV) or a hepatitisvirus; meets only the SBP<90 mmHg inclusion criterion set forth above,and does not have shock in the attending physician's or principalinvestigator's opinion.

After providing informed consent, an EDTA anti-coagulated blood sample(10 mL) and a urine sample (25-30 mL) are collected from each patient.Blood and urine samples are then collected at 4 (±0.5) and 8 (±1) hoursafter contrast administration (if applicable); at 12 (±1), 24 (±2), and48 (±2) hours after enrollment, and thereafter daily up to day 7 to day14 while the subject is hospitalized. Blood is collected via directvenipuncture or via other available venous access, such as an existingfemoral sheath, central venous line, peripheral intravenous line orhep-lock. These study blood samples are processed to plasma at theclinical site, frozen and shipped to Astute Medical, Inc., San Diego,Calif. The study urine samples are frozen and shipped to Astute Medical,Inc.

Example 4 Immunoassay Format

Analytes are is measured using standard sandwich enzyme immunoassaytechniques. A first antibody which binds the analyte is immobilized inwells of a 96 well polystyrene microplate. Analyte standards and testsamples are pipetted into the appropriate wells and any analyte presentis bound by the immobilized antibody. After washing away any unboundsubstances, a horseradish peroxidase-conjugated second antibody whichbinds the analyte is added to the wells, thereby forming sandwichcomplexes with the analyte (if present) and the first antibody.Following a wash to remove any unbound antibody-enzyme reagent, asubstrate solution comprising tetramethylbenzidine and hydrogen peroxideis added to the wells. Color develops in proportion to the amount ofanalyte present in the sample. The color development is stopped and theintensity of the color is measured at 540 nm or 570 nm. An analyteconcentration is assigned to the test sample by comparison to a standardcurve determined from the analyte standards.

Concentrations are expressed in the following examples as cytochromec—ng/mL; and insulin-like growth factor IA—ng/mL.

Example 5 Apparently Healthy Donor and Chronic Disease Patient Samples

Human urine samples from donors with no known chronic or acute disease(“Apparently Healthy Donors”) were purchased from two vendors (GoldenWest Biologicals, Inc., 27625 Commerce Center Dr., Temecula, Calif.92590 and Virginia Medical Research, Inc., 915 First Colonial Rd.,Virginia Beach, Va. 23454). The urine samples were shipped and storedfrozen at less than −20° C. The vendors supplied demographic informationfor the individual donors including gender, race (Black/White), smokingstatus and age.

Human urine samples from donors with various chronic diseases (“ChronicDisease Patients”) including congestive heart failure, coronary arterydisease, chronic kidney disease, chronic obstructive pulmonary disease,diabetes mellitus and hypertension were purchased from Virginia MedicalResearch, Inc., 915 First Colonial Rd., Virginia Beach, Va. 23454. Theurine samples were shipped and stored frozen at less than −20 degreescentigrade. The vendor provided a case report form for each individualdonor with age, gender, race (Black/White), smoking status and alcoholuse, height, weight, chronic disease(s) diagnosis, current medicationsand previous surgeries.

Example 6 Kidney Injury Markers for Evaluating Renal Status in Patientsat RIFLE Stage 0

Patients from the intensive care unit (ICU) were classified by kidneystatus as non-injury (0), risk of injury (R), injury (I), and failure(F) according to the maximum stage reached within 7 days of enrollmentas determined by the RIFLE criteria.

Two cohorts were defined as (Cohort 1) patients that did not progressbeyond stage 0, and (Cohort 2) patients that reached stage R, I, or Fwithin 10 days. To address normal marker fluctuations that occur withinpatients at the ICU and thereby assess utility for monitoring AKIstatus, marker levels in urine samples collected for Cohort 1. Markerconcentrations were measured in urine samples collected from a subjectat 0, 24 hours, and 48 hours prior to reaching stage R, I or F in Cohort2. In the following tables, the time “prior max stage” represents thetime at which a sample is collected, relative to the time a particularpatient reaches the lowest disease stage as defined for that cohort,binned into three groups which are +/−12 hours. For example, 24 hr priorfor this example (0 vs R, I, F) would mean 24 hr (+/−12 hours) prior toreaching stage R (or I if no sample at R, or F if no sample at R or I).

Each marker was measured by standard immunoassay methods usingcommercially available assay reagents. A receiver operatingcharacteristic (ROC) curve was generated for each marker and the areaunder each ROC curve (AUC) was determined. Patients in Cohort 2 werealso separated according to the reason for adjudication to stage R, I,or F as being based on serum creatinine measurements, being based onurine output, or being based on either serum creatinine measurements orurine output. That is, for those patients adjudicated to stage R, I, orF on the basis of serum creatinine measurements alone, the stage 0cohort may have included patients adjudicated to stage R, I, or F on thebasis of urine output; for those patients adjudicated to stage R, I, orF on the basis of urine output alone, the stage 0 cohort may haveincluded patients adjudicated to stage R, I, or F on the basis of serumcreatinine measurements; and for those patients adjudicated to stage R,I, or F on the basis of serum creatinine measurements or urine output,the stage 0 cohort contains only patients in stage 0 for both serumcreatinine measurements and urine output. Also, for those patientsadjudicated to stage R, I, or F on the basis of serum creatininemeasurements or urine output, the adjudication method which yielded themost severe RIFLE stage was used.

The following descriptive statistics were obtained:

Insulin-Like Growth Factor IA:

0 hr prior to AKI stage 24 hr prior to AKI stage 48 hr prior to AKIstage Cohort 1 Cohort 2 Cohort 1 Cohort 2 Cohort 1 Cohort 2 sCr or UOmedian 13.000 22.500 13.000 19.500 13.000 19.900 average 13.929 22.44713.929 24.367 13.929 26.934 stdev 9.508 12.754 9.508 37.910 9.508 41.727p (t-test) 0.000 0.000 0.000 min 0.016 0.016 0.016 0.016 0.016 0.016 max74.200 45.900 74.200 276.000 74.200 211.000 n (Samp) 216 38 216 51 21623 n (Pat) 77 38 77 51 77 23 sCr only median 13.900 17.950 13.900 18.90013.900 27.000 average 16.505 19.058 16.505 22.041 16.505 22.960 stdev19.756 14.223 19.756 15.186 19.756 10.917 p (t-test) 0.610 0.207 0.282min 0.016 0.016 0.016 0.016 0.016 3.510 max 276.000 47.500 276.00055.200 276.000 36.700 n (Samp) 375 16 375 21 375 11 n (Pat) 127 16 12721 127 11 UO only median 13.200 25.100 13.200 22.300 13.200 19.900average 13.791 23.844 13.791 25.702 13.791 26.071 stdev 8.309 12.5548.309 40.207 8.309 41.686 p (t-test) 0.000 0.000 0.001 min 0.016 0.0160.016 0.016 0.016 0.016 max 44.200 45.900 44.200 276.000 44.200 211.000n (Samp) 181 34 181 45 181 23 n (Pat) 61 34 61 45 61 23

In the following tables, the ability to distinguish cohort 1 (subjectsremaining in RIFLE 0) from Cohort 2 (subjects progressing to RIFLE R, Ior F) was determined using ROC analysis. SE is the standard error of theAUC, n is the number of sample or individual patients (“pts,” asindicated). Standard errors were calculated as described in Hanley, J.A., and McNeil, B. J., The meaning and use of the area under a receiveroperating characteristic (ROC) curve. Radiology (1982) 143: 29-36; pvalues were calculated with a two-tailed Z-test.

Insulin-Like Growth Factor IA:

Cohort 1 v Cohort 2, adjudicated on serum creatinine measurements orurine output Time prior max stage AUC SE n_(Cohort 1) n_(Cohort 2) P  0hours 0.70 0.050 216 38 0.000 24 hours 0.65 0.045 216 51 0.001 48 hours0.65 0.065 216 23 0.025

Cohort 1 v Cohort 2, adjudicated on serum creatinine Time prior maxstage AUC SE n_(Cohort 1) n_(Cohort 2) P  0 hours 0.56 0.076 375 160.409 24 hours 0.63 0.067 375 21 0.047 48 hours 0.70 0.089 375 11 0.023

Cohort 1 v Cohort 2, adjudicated on urine output Time prior max stageAUC SE n_(Cohort 1) n_(Cohort 2) P  0 hours 0.74 0.052 181 34 0.000 24hours 0.66 0.048 181 45 0.001 48 hours 0.63 0.065 181 23 0.054

Various threshold (or “cutoff”) concentrations were selected, and theassociated sensitivity and specificity for distinguishing cohort 1 fromcohort 2, as shown in the following tables. OR is the odds ratiocalculated for the particular cutoff concentration, and 95% CI is theconfidence interval for the odds ratio:

Insulin-Like Growth Factor IA:

Time prior Cutoff Quar- 95% CI AKI stage value sens spec tile OR of ORsCr or UO 0 hours 15.6 71% 65% 1 6.99 82% 21% 2 0.2 0.1 0.8 4.8 92% 14%3 0.6 0.3 1.2 16.9 66% 70% 4 3.9 2.6 5.8 20.4 61% 80% 24 47% 90% 24hours 11.7 71% 45% 1 6.99 80% 21% 2 0.7 0.4 1.1 4.53 90% 13% 3 0.7 0.41.1 16.9 57% 70% 4 2.8 2.0 3.9 20.4 49% 80% 24 37% 90% 48 hours 12.8 74%50% 1 8.37 83% 26% 2 0.7 0.2 2.4 1.29 91%  9% 3 1.0 0.3 2.8 16.9 57% 70%4 3.4 1.7 7.1 20.4 48% 80% 24 30% 90% sCr only 0 hours 8.37 75% 25% 16.99 81% 21% 2 0.5 0.1 2.2 0 100%   0% 3 1.3 0.5 3.1 19.5 50% 70% 4 1.30.5 3.1 23.5 31% 80% 29.1 19% 90% 24 hours 14.2 71% 53% 1 9.65 81% 30% 20.5 0.1 2.2 5.29 90% 16% 3 1.5 0.6 3.6 19.5 48% 70% 4 2.4 1.1 5.0 23.543% 80% 29.1 24% 90% 48 hours 15.6 73% 58% 1 15.3 82% 56% 2 1.0 0.0 52.08.74 91% 25% 3 3.1 0.2 43.6 19.5 64% 70% 4 6.3 0.6 64.3 23.5 55% 80%29.1 36% 90% UO only 0 hours 16.5 71% 69% 1 10.5 82% 37% 2 0.8 0.3 2.05.2 91% 15% 3 0.8 0.3 2.0 16.9 68% 70% 4 6.1 3.4 11.0 21.2 65% 80% 23.853% 90% 24 hours 11.7 71% 43% 1 6.99 80% 20% 2 0.6 0.4 1.1 2.15 91%  8%3 0.5 0.2 0.9 16.9 60% 70% 4 3.1 2.1 4.6 21.2 51% 80% 23.8 44% 90% 48hours 11.8 74% 44% 1 8.37 83% 27% 2 1.0 0.3 2.9 1.29 91%  8% 3 1.0 0.32.9 16.9 57% 70% 4 3.2 1.5 6.9 21.2 39% 80% 23.8 22% 90%

Example 7 Kidney Injury Markers for Evaluating Renal Status in Patientsat RIFLE Stages 0 and R

Patients were classified and analyzed as described in Example 6.However, patients that reached stage R but did not progress to stage Ior F were grouped with patients from non-injury stage 0 in Cohort 1.Cohort 2 in this example included only patients that progressed to stageI or F. Marker concentrations in urine samples were included forCohort 1. Marker concentrations in urine samples collected within 0, 24,and 48 hours of reaching stage I or F were included for Cohort 2.

The following descriptive statistics were obtained:

Cytochrome C:

0 hr prior to AKI stage 24 hr prior to AKI stage 48 hr prior to AKIstage Cohort 1 Cohort 2 Cohort 1 Cohort 2 Cohort 1 Cohort 2 sCr or UOmedian 0.073 0.000 0.073 0.378 0.073 0.000 average 0.309 0.042 0.3090.670 0.309 1.303 stdev 0.723 na 0.723 0.736 0.723 na p (t-test) na0.068 na min 0.000 0.042 0.000 0.000 0.000 1.303 max 5.092 0.042 5.0922.416 5.092 1.303 n (Samp) 99 1 99 16 99 1 n (Pat) 75 1 75 16 75 1 sCronly median 0.074 na 0.074 0.806 0.074 na average 0.354 na 0.354 0.7860.354 na stdev 0.736 na 0.736 0.504 0.736 na p (t-test) na 0.315 na min0.000 na 0.000 0.272 0.000 na max 5.092 na 5.092 1.280 5.092 na n (Samp)114 0 114 3 114 0 n (Pat) 88 0 88 3 88 0 UO only median 0.075 0.0000.075 0.198 0.075 1.291 average 0.344 0.042 0.344 0.909 0.344 1.291stdev 0.780 na 0.780 1.354 0.780 0.017 p (t-test) na 0.026 0.091 min0.000 0.042 0.000 0.000 0.000 1.280 max 5.092 0.042 5.092 5.004 5.0921.303 n (Samp) 82 1 82 15 82 2 n (Pat) 62 1 62 15 62 2

Insulin-Like Growth Factor IA:

0 hr prior to AKI stage 24 hr prior to AKI stage 48 hr prior to AKIstage Cohort 1 Cohort 2 Cohort 1 Cohort 2 Cohort 1 Cohort 2 sCr or UOmedian 13.900 20.500 13.900 22.500 13.900 23.700 average 16.355 20.80716.355 22.700 16.355 20.701 stdev 20.194 10.605 20.194 13.563 20.1948.689 p (t-test) 0.317 0.123 0.440 min 0.016 0.016 0.016 0.016 0.0160.016 max 276.000 36.100 276.000 52.600 276.000 31.600 n (Samp) 351 21351 25 351 13 n (Pat) 121 21 121 25 121 13 sCr only median 13.900 15.60013.900 21.750 13.900 34.100 average 16.402 19.160 16.402 23.662 16.40237.360 stdev 18.883 10.494 18.883 12.080 18.883 12.169 p (t-test) 0.7450.349 0.014 min 0.016 10.100 0.016 9.670 0.016 25.300 max 276.000 34.800276.000 38.900 276.000 52.600 n (Samp) 428 5 428 6 428 5 n (Pat) 146 5146 6 146 5 UO only median 14.000 21.400 14.000 22.400 14.000 21.500average 16.678 20.991 16.678 21.893 16.678 19.601 stdev 21.367 10.86521.367 13.529 21.367 8.611 p (t-test) 0.372 0.261 0.624 min 0.016 0.0160.016 0.016 0.016 0.016 max 276.000 36.100 276.000 52.600 276.000 31.600n (Samp) 294 20 294 22 294 13 n (Pat) 96 20 96 22 96 13

In the following tables, the ability to distinguish cohort 1 (subjectsremaining in RIFLE 0 or R) from Cohort 2 (subjects progressing to RIFLEI or F) was determined using ROC analysis.

Cytochrome C:

Cohort 1 v Cohort 2, adjudicated on serum creatinine measurements orurine output Time prior max stage AUC SE n_(Cohort 1) n_(Cohort 2) P  0hours 0.34 0.244 99 1 1.480 24 hours 0.67 0.078 99 16 0.025 48 hours0.95 0.154 99 1 0.003

Cohort 1 v Cohort 2, adjudicated on serum creatinine Time prior maxstage AUC SE n_(Cohort 1) n_(Cohort 2) P  0 hours nd nd 114 0 0.211 24hours 0.83 0.147 114 3 0.025 48 hours nd nd 114 0 0.211

Cohort 1 v Cohort 2, adjudicated on urine output Time prior max stageAUC SE n_(Cohort 1) n_(Cohort 2) P  0 hours 0.34 0.243 82 1 1.485 24hours 0.66 0.082 82 15 0.052 48 hours 0.93 0.124 82 2 0.000

Insulin-Like Growth Factor IA:

Cohort 1 v Cohort 2, adjudicated on serum creatinine measurements orurine output Time prior max stage AUC SE n_(Cohort 1) n_(Cohort 2) P  0hours 0.66 0.066 351 21 0.015 24 hours 0.67 0.061 351 25 0.005 48 hours0.70 0.082 351 13 0.015

Cohort 1 v Cohort 2, adjudicated on serum creatinine Time prior maxstage AUC SE n_(Cohort 1) n_(Cohort 2) P  0 hours 0.61 0.135 428 5 0.42524 hours 0.70 0.120 428 6 0.093 48 hours 0.93 0.080 428 5 0.000

Cohort 1 v Cohort 2, adjudicated on urine output Time prior max stageAUC SE n_(Cohort 1) n_(Cohort 2) P  0 hours 0.66 0.068 294 20 0.022 24hours 0.65 0.065 294 22 0.019 48 hours 0.66 0.084 294 13 0.054

Various threshold (or “cutoff”) concentrations were selected, and theassociated sensitivity and specificity for distinguishing cohort 1 fromcohort 2, as shown in the following tables. OR is the odds ratiocalculated for the particular cutoff concentration, and 95% CI is theconfidence interval for the odds ratio:

Cytochrome C:

Time prior Cutoff Quar- 95% CI AKI stage value sens spec tile OR of ORsCr or UO 0 hours 0.041446555 100% 34% 1 0.041446555 100% 34% 2 na na na0.041446555 100% 34% 3 na na na 0.16129622  0% 71% 4 na na na0.406081141  0% 81% 0.895276879  0% 91% 24 hours 0.074532249  75% 53% 10.026298431  81% 30% 2 1.0 0.1 7.9 0 100%  0% 3 2.1 0.4 10.6 0.16129622 63% 71% 4 5.0 1.2 20.0 0.406081141  50% 81% 0.895276879  31% 91% 48hours 1.301851365 100% 95% 1 1.301851365 100% 95% 2 na na na 1.301851365100% 95% 3 na na na 0.16129622 100% 71% 4 na na na 0.406081141 100% 81%0.895276879 100% 91% sCr only 0 hours 0 na na 1 0 na na 2 na na na 0 nana 3 na na na 0 na na 4 na na na 0 na na 0 na na 24 hours 0.246456888100% 73% 1 0.246456888 100% 73% 2 na na na 0.246456888 100% 73% 3 na nana 0.210408645 100% 70% 4 na na na 0.463086389  67% 81% 1.234702778  33%90% 48 hours 0 na na 1 0 na na 2 na na na 0 na na 3 na na na 0 na na 4na na na 0 na na 0 na na UO only 0 hours 0.02074757 100% 34% 10.02074757 100% 34% 2 na na na 0.02074757 100% 34% 3 na na na0.213250733  0% 71% 4 na na na 0.43645974  0% 80% 0.895276879  0% 90% 24hours 0.072560528  73% 50% 1 0.02074757  80% 34% 2 1.6 0.3 9.7 0 100% 0% 3 1.6 0.3 9.7 0.213250733  47% 71% 4 4.3 1.0 18.4 0.43645974  47%80% 0.895276879  33% 90% 48 hours 1.168655354 100% 93% 1 1.168655354100% 93% 2 na na na 1.168655354 100% 93% 3 na na na 0.213250733 100% 71%4 na na na 0.43645974 100% 80% 0.895276879 100% 90%

Insulin-Like Growth Factor IA:

Time prior Cutoff Quar- 95% CI AKI stage value sens spec tile OR of ORsCr or UO 0 hours 0.041446555 15.5 71% 59% 1 0.041446555 10.6 81% 35% 22.0 0.5 0.041446555  9.7 90% 31% 3 2.6 0.6 0.16129622 19.3 57% 70% 4 5.51.6 0.406081141 22.5 43% 80% 0.895276879 28   33% 90% 24 hours0.074532249 13.6 76% 49% 1 0.026298431 10.7 80% 35% 2 1.0 0.4 0 4.53 92%14% 3 0.7 0.2 0.16129622 19.3 60% 70% 4 3.9 2.0 0.406081141 22.5 48% 80%0.895276879 28   36% 90% 48 hours 1.301851365 17.1 77% 65% 1 1.30185136512.8 85% 45% 2 2.0 0.1 1.301851365 10.4 92% 34% 3 3.1 0.2 0.1612962219.3 69% 70% 4 7.5 0.8 0.406081141 22.5 54% 80% 0.895276879 28   15% 90%sCr only 0 hours 10.6 80% 35% 1 10.6 80% 35% 2 na na na 9.95 100%  32% 3na na na 20.3 40% 70% 4 na na na 23.6 40% 80% 29.1 20% 90% 24 hours 13.683% 48% 1 13.6 83% 48% 2 na na na 9.65 100%  30% 3 na na na 20.3 50% 70%4 na na na 23.6 50% 80% 29.1 33% 90% 48 hours 27.2 80% 87% 1 27.2 80%87% 2 na na na 24.9 100%  85% 3 na na na 20.3 100%  70% 4 na na na 23.6100%  80% 29.1 60% 90% UO only 0 hours 16.5 70% 61% 1 10.6 80% 34% 2 1.00.3 3.8 8.02 90% 24% 3 1.4 0.4 4.5 19.5 60% 71% 4 3.6 1.5 8.9 22.7 45%80% 28.3 25% 90% 24 hours 13.6 73% 48% 1 9.95 82% 31% 2 0.7 0.2 2.4 4.3391% 13% 3 0.7 0.2 2.4 19.5 64% 71% 4 3.4 1.7 6.8 22.7 45% 80% 28.3 32%90% 48 hours 13.6 77% 48% 1 12.8 85% 43% 2 3.0 0.2 43.7 10.4 92% 33% 33.0 0.2 43.7 19.5 62% 71% 4 6.3 0.6 65.8 22.7 46% 80% 28.3 15% 90%

Example 8 Kidney Injury Markers for Evaluating Renal Status in Patientsat RIFLE Stage 0

Patients from the intensive care unit (ICU) were classified by kidneystatus as non-injury (O), risk of injury (R), injury (I), and failure(F) according to the maximum stage reached within 7 days of enrollmentas determined by the RIFLE criteria.

Two cohorts were defined as (Cohort 1) patients that did not progressbeyond stage 0, and (Cohort 2) patients that reached stage R, I, or Fwithin 10 days. To address normal marker fluctuations that occur withinpatients at the ICU and thereby assess utility for monitoring AKIstatus, marker levels in blood samples collected for Cohort 1. Markerconcentrations were measured in the plasma component of the bloodsamples collected from a subject at 0, 24 hours, and 48 hours prior toreaching stage R, I or F in Cohort 2. In the following tables, the time“prior max stage” represents the time at which a sample is collected,relative to the time a particular patient reaches the lowest diseasestage as defined for that cohort, binned into three groups which are+/−12 hours. For example, 24 hr prior for this example (0 vs R, I, F)would mean 24 hr (+/−12 hours) prior to reaching stage R (or I if nosample at R, or F if no sample at R or I).

Each marker was measured by standard immunoassay methods usingcommercially available assay reagents. A receiver operatingcharacteristic (ROC) curve was generated for each marker and the areaunder each ROC curve (AUC) was determined. Patients in Cohort 2 werealso separated according to the reason for adjudication to stage R, I,or F as being based on serum creatinine measurements (sCr), being basedon urine output (UO), or being based on either serum creatininemeasurements or urine output. That is, for those patients adjudicated tostage R, I, or F on the basis of serum creatinine measurements alone,the stage 0 cohort may have included patients adjudicated to stage R, I,or F on the basis of urine output; for those patients adjudicated tostage R, I, or F on the basis of urine output alone, the stage 0 cohortmay have included patients adjudicated to stage R, I, or F on the basisof serum creatinine measurements; and for those patients adjudicated tostage R, I, or F on the basis of serum creatinine measurements or urineoutput, the stage 0 cohort contains only patients in stage 0 for bothserum creatinine measurements and urine output. Also, for those patientsadjudicated to stage R, I, or F on the basis of serum creatininemeasurements or urine output, the adjudication method which yielded themost severe RIFLE stage was used.

The following descriptive statistics were obtained:

Insulin-Like Growth Factor IA:

0 hr prior to AKI stage 24 hr prior to AKI stage 48 hr prior to AKIstage Cohort 1 Cohort 2 Cohort 1 Cohort 2 Cohort 1 Cohort 2 sCr or UOmedian 0.040 0.040 0.040 0.040 0.040 0.040 average 10.284 13.296 10.28411.057 10.284 13.485 stdev 23.528 33.608 23.528 23.286 23.528 20.428 p(t-test) 0.510 0.832 0.539 min 0.040 0.040 0.040 0.040 0.040 0.040 max193.000 191.000 193.000 119.000 193.000 60.800 n (Samp) 221 35 221 51221 22 n (Pat) 80 35 80 51 80 22 sCr only median 0.040 0.040 0.040 0.0400.040 0.040 average 10.248 3.323 10.248 10.330 10.248 14.448 stdev25.223 5.857 25.223 27.138 25.223 23.219 p (t-test) 0.274 0.988 0.603min 0.040 0.040 0.040 0.040 0.040 0.040 max 204.000 17.100 204.000119.000 204.000 49.500 n (Samp) 386 16 386 21 386 10 n (Pat) 129 16 12921 129 10 UO only median 0.040 0.040 0.040 0.040 0.040 0.040 average9.875 13.038 9.875 8.760 9.875 11.770 stdev 22.770 34.154 22.770 17.86322.770 19.241 p (t-test) 0.496 0.760 0.714 min 0.040 0.040 0.040 0.0400.040 0.040 max 193.000 191.000 193.000 71.200 193.000 60.800 n (Samp)183 34 183 45 183 21 n (Pat) 65 34 65 45 65 21

In the following tables, the ability to distinguish cohort 1 (subjectsremaining in RIFLE 0) from Cohort 2 (subjects progressing to RIFLE R, Ior F) was determined using ROC analysis. SE is the standard error of theAUC, n is the number of sample or individual patients (“pts,” asindicated). Standard errors were calculated as described in Hanley, J.A., and McNeil, B. J., The meaning and use of the area under a receiveroperating characteristic (ROC) curve. Radiology (1982) 143: 29-36; pvalues were calculated with a two-tailed Z-test.

Insulin-Like Growth Factor IA:

Cohort 1 v Cohort 2, adjudicated on serum creatinine measurements orurine output Time prior max stage AUC SE n_(Cohort 1) n_(Cohort 2) P  0hours 0.51 0.053 221 35 0.837 24 hours 0.47 0.044 221 51 1.558 48 hours0.52 0.065 221 22 0.730

Cohort 1 v Cohort 2, adjudicated on serum creatinine Time prior maxstage AUC SE n_(Cohort 1) n_(Cohort 2) P  0 hours 0.45 0.071 386 161.511 24 hours 0.45 0.062 386 21 1.591 48 hours 0.50 0.093 386 10 0.980

Cohort 1 v Cohort 2, adjudicated on urine output Time prior max stageAUC SE n_(Cohort 1) n_(Cohort 2) P  0 hours 0.50 0.054 183 34 0.968 24hours 0.47 0.047 183 45 1.491 48 hours 0.51 0.067 183 21 0.852

Various threshold (or “cutoff”) concentrations were selected, and theassociated sensitivity and specificity for distinguishing cohort 1 fromcohort 2, as shown in the following tables. OR is the odds ratiocalculated for the particular cutoff concentration, and 95% CI is theconfidence interval for the odds ratio:

Insulin-Like Growth Factor IA:

Time prior Cutoff Quar- 95% CI AKI stage value sens spec tile OR of ORsCr or UO 0 hours 0 100%  0% 1 0 100%  0% 2 3.3 1.8 6.0 0 100%  0% 3 1.20.6 2.7 7.05  34% 70% 4 2.2 1.1 4.2 15.2  23% 80% 30.1  14% 90% 24 hours0 100%  0% 1 0 100%  0% 2 0.3 0.2 0.6 0 100%  0% 3 0.7 0.5 1.1 7.05  29%70% 4 1.7 1.3 2.4 15.2  20% 80% 30.1  16% 90% 48 hours 0 100%  0% 1 0100%  0% 2 6.4 1.9 21.9 0 100%  0% 3 0.5 0.0 9.8 7.05  36% 70% 4 4.4 1.216.0 15.2  32% 80% 30.1  23% 90% sCr only 0 hours 0 100%  0% 1 0 100% 0% 2 1.5 0.3 8.2 0 100%  0% 3 6.1 1.8 20.1 5.86  25% 70% 4 0.0 0.065535.0 13.5  13% 80% 32.8   0% 90% 24 hours 0 100%  0% 1 0 100%  0% 20.0 0.0 65535.0 0 100%  0% 3 3.6 2.1 6.3 5.86  24% 70% 4 0.0 0.0 65535.013.5  19% 80% 32.8  10% 90% 48 hours 0 100%  0% 1 0 100%  0% 2 na na na0 100%  0% 3 na na na 5.86  30% 70% 4 na na na 13.5  30% 80% 32.8  30%90% UO only 0 hours 0 100%  0% 1 0 100%  0% 2 na na na 0 100%  0% 3 nana na 5.33  35% 70% 4 na na na 16.6  21% 80% 30.6  12% 90% 24 hours 0100%  0% 1 0 100%  0% 2 0.2 0.1 0.6 0 100%  0% 3 1.9 1.3 2.8 5.33  29%70% 4 1.2 0.8 1.9 16.6  16% 80% 30.6  13% 90% 48 hours 0 100%  0% 1 0100%  0% 2 1.0 0.5 2.1 0 100%  0% 3 0.3 0.1 1.2 5.33  33% 70% 4 1.2 0.62.4 16.6  29% 80% 30.6  19% 90%

While the invention has been described and exemplified in sufficientdetail for those skilled in this art to make and use it, variousalternatives, modifications, and improvements should be apparent withoutdeparting from the spirit and scope of the invention. The examplesprovided herein are representative of preferred embodiments, areexemplary, and are not intended as limitations on the scope of theinvention. Modifications therein and other uses will occur to thoseskilled in the art. These modifications are encompassed within thespirit of the invention and are defined by the scope of the claims.

It will be readily apparent to a person skilled in the art that varyingsubstitutions and modifications may be made to the invention disclosedherein without departing from the scope and spirit of the invention.

All patents and publications mentioned in the specification areindicative of the levels of those of ordinary skill in the art to whichthe invention pertains. All patents and publications are hereinincorporated by reference to the same extent as if each individualpublication was specifically and individually indicated to beincorporated by reference.

The invention illustratively described herein suitably may be practicedin the absence of any element or elements, limitation or limitationswhich is not specifically disclosed herein. Thus, for example, in eachinstance herein any of the terms “comprising”, “consisting essentiallyof” and “consisting of” may be replaced with either of the other twoterms. The terms and expressions which have been employed are used asterms of description and not of limitation, and there is no intentionthat in the use of such terms and expressions of excluding anyequivalents of the features shown and described or portions thereof, butit is recognized that various modifications are possible within thescope of the invention claimed. Thus, it should be understood thatalthough the present invention has been specifically disclosed bypreferred embodiments and optional features, modification and variationof the concepts herein disclosed may be resorted to by those skilled inthe art, and that such modifications and variations are considered to bewithin the scope of this invention as defined by the appended claims.

Other embodiments are set forth within the following claims.

1. A method for evaluating renal status in a subject, comprising:performing one or more assays configured to detect a kidney injurymarker selected from the group consisting of cytochrome c andinsulin-like growth factor IA on a body fluid sample obtained from thesubject to provide one or more assay results; and correlating the assayresult(s) to the renal status of the subject, wherein said correlationstep comprises correlating the assay result(s) to one or more of riskstratification, staging, prognosis, classifying and monitoring of therenal status of the subject.
 2. A method according to claim 1, whereinsaid correlating step comprises assigning a likelihood of one or morefuture changes in renal status to the subject based on the assayresult(s).
 3. A method according to claim 2, wherein said one or morefuture changes in renal status comprise one or more of a future injuryto renal function, future reduced renal function, future improvement inrenal function, and future acute renal failure (ARF).
 4. A methodaccording to claim 3, wherein said assay result(s) comprise one or moreof: (i) a measured concentration of cytochrome c, and (ii) a measuredconcentration of insulin-like growth factor IA, and said correlationstep comprises, for each assay result, comparing said measureconcentration to a threshold concentration, and for a positive goingmarker, assigning an increased likelihood of suffering a future injuryto renal function, future reduced renal function, future ARF, or afuture improvement in renal function to the subject when the measuredconcentration is above the threshold, relative to a likelihood assignedwhen the measured concentration is below the threshold or assigning adecreased likelihood of suffering a future injury to renal function,future reduced renal function, future ARF, or a future improvement inrenal function to the subject when the measured concentration is belowthe threshold, relative to a likelihood assigned when the measuredconcentration is above the threshold, or for a negative going marker,assigning an increased likelihood of suffering a future injury to renalfunction, future reduced renal function, future ARF, or a futureimprovement in renal function to the subject when the measuredconcentration is below the threshold, relative to a likelihood assignedwhen the measured concentration is above the threshold or assigning adecreased likelihood of suffering a future injury to renal function,future reduced renal function, future ARF, or a future improvement inrenal function to the subject when the measured concentration is abovethe threshold, relative to a likelihood assigned when the measuredconcentration is below the threshold.
 5. A method according to claim 2,wherein said one or more future changes in renal status comprise aclinical outcome related to a renal injury suffered by the subject.
 6. Amethod according to claim 1, wherein said assay result(s) comprise oneor more of: (i) a measured concentration of cytochrome c, and (ii) ameasured concentration of insulin-like growth factor IA, and saidcorrelation step comprises, for each assay result, comparing saidmeasure concentration to a threshold concentration, and for a positivegoing marker, assigning an increased likelihood of subsequent acutekidney injury, worsening stage of AKI, mortality, need for renalreplacement therapy, need for withdrawal of renal toxins, end stagerenal disease, heart failure, stroke, myocardial infarction, or chronickidney disease to the subject when the measured concentration is abovethe threshold, relative to a likelihood assigned when the measuredconcentration is below the threshold, or assigning a decreasedlikelihood of subsequent acute kidney injury, worsening stage of AKI,mortality, need for renal replacement therapy, need for withdrawal ofrenal toxins, end stage renal disease, heart failure, stroke, myocardialinfarction, or chronic kidney disease to the subject when the measuredconcentration is below the threshold, relative to a likelihood assignedwhen the measured concentration is above the threshold, or for anegative going marker, assigning an increased likelihood of subsequentacute kidney injury, worsening stage of AKI, mortality, need for renalreplacement therapy, need for withdrawal of renal toxins, end stagerenal disease, heart failure, stroke, myocardial infarction, or chronickidney disease to the subject when the measured concentration is belowthe threshold, relative to a likelihood assigned when the measuredconcentration is above the threshold, or assigning a decreasedlikelihood of subsequent acute kidney injury, worsening stage of AKI,mortality, need for renal replacement therapy, need for withdrawal ofrenal toxins, end stage renal disease, heart failure, stroke, myocardialinfarction, or chronic kidney disease to the subject when the measuredconcentration is above the threshold, relative to a likelihood assignedwhen the measured concentration is below the threshold.
 7. A methodaccording to claim 2, wherein the likelihood of one or more futurechanges in renal status is that an event of interest is more or lesslikely to occur within 30 days of the time at which the body fluidsample is obtained from the subject.
 8. A method according to claim 7,wherein the likelihood of one or more future changes in renal status isthat an event of interest is more or less likely to occur within aperiod selected from the group consisting of 21 days, 14 days, 7 days, 5days, 96 hours, 72 hours, 48 hours, 36 hours, 24 hours, and 12 hours. 9.A method according to claim 1, wherein the subject is selected forevaluation of renal status based on the pre-existence in the subject ofone or more known risk factors for prerenal, intrinsic renal, orpostrenal ARF.
 10. A method according to claim 1, wherein the subject isselected for evaluation of renal status based on an existing diagnosisof one or more of congestive heart failure, preeclampsia, eclampsia,diabetes mellitus, hypertension, coronary artery disease, proteinuria,renal insufficiency, glomerular filtration below the normal range,cirrhosis, serum creatinine above the normal range, sepsis, injury torenal function, reduced renal function, or ARF, or based on undergoingor having undergone major vascular surgery, coronary artery bypass, orother cardiac surgery, or based on exposure to NSAIDs, cyclosporines,tacrolimus, aminoglycosides, foscarnet, ethylene glycol, hemoglobin,myoglobin, ifosfamide, heavy metals, methotrexate, radiopaque contrastagents, or streptozotocin.
 11. A method according to claim 1, whereinsaid correlating step comprises assessing whether or not renal functionis improving or worsening in a subject who has suffered from an injuryto renal function, reduced renal function, or ARF based on the assayresult(s).
 12. A method according to claim 11, wherein said assayresult(s) comprise one or more of: (i) a measured concentration ofcytochrome c, and (ii) a measured concentration of insulin-like growthfactor IA, and said correlation step comprises, for each assay result,comparing said measure concentration to a threshold concentration, andfor a positive going marker, assigning a worsening of renal function tothe subject when the measured concentration is above the threshold, orassigning an improvement of renal function when the measuredconcentration is below the threshold, or for a negative going marker,assigning a worsening of renal function to the subject when the measuredconcentration is below the threshold, or assigning an improvement ofrenal function when the measured concentration is above the threshold.13. A method according to claim 1, wherein said method is a method ofassigning a risk of the future occurrence or nonoccurrence of an injuryto renal function in said subject.
 14. A method according to claim 1,wherein said method is a method of assigning a risk of the futureoccurrence or nonoccurrence of reduced renal function in said subject.15. A method according to claim 1, wherein said method is a method ofassigning a risk of the future occurrence or nonoccurrence of acuterenal failure in said subject.
 16. A method according to claim 1,wherein said method is a method of assigning a risk of the futureoccurrence or nonoccurrence of a need for renal replacement therapy insaid subject.
 17. A method according to claim 1, wherein said method isa method of assigning a risk of the future occurrence or nonoccurrenceof a need for renal transplantation in said subject.
 18. A methodaccording to claim 4, wherein said one or more future changes in renalstatus comprise one or more of a future injury to renal function, futurereduced renal function, future improvement in renal function, and futureacute renal failure (ARF) within 72 hours of the time at which the bodyfluid sample is obtained.
 19. A method according to claim 4, whereinsaid one or more future changes in renal status comprise one or more ofa future injury to renal function, future reduced renal function, futureimprovement in renal function, and future acute renal failure (ARF)within 48 hours of the time at which the body fluid sample is obtained.20. A method according to claim 4, wherein said one or more futurechanges in renal status comprise one or more of a future injury to renalfunction, future reduced renal function, future improvement in renalfunction, and future acute renal failure (ARF) within 72 hours of thetime at which the body fluid sample is obtained.
 21. A method accordingto claim 4, wherein said one or more future changes in renal statuscomprise one or more of a future injury to renal function, futurereduced renal function, future improvement in renal function, and futureacute renal failure (ARF) within 48 hours of the time at which the bodyfluid sample is obtained.
 22. A method according to claim 4, whereinsaid one or more future changes in renal status comprise one or more ofa future injury to renal function, future reduced renal function, futureimprovement in renal function, and future acute renal failure (ARF)within 24 hours of the time at which the body fluid sample is obtained.23. Use of one or more kidney injury markers selected from the groupconsisting of cytochrome c and insulin-like growth factor IA for one ormore of risk stratification, staging, prognosis, classifying andmonitoring of the renal status of a subject.
 24. Use of one or morekidney injury markers selected from the group consisting of cytochrome cand insulin-like growth factor IA for risk stratification, staging,prognosis, classifying and monitoring of the renal status of a subjectsuffering from an acute renal injury.
 25. A method according to claim 6,wherein the increased or decreased likelihood of subsequent acute kidneyinjury, worsening stage of AKI, mortality, need for renal replacementtherapy, need for withdrawal of renal toxins, end stage renal disease,heart failure, stroke, myocardial infarction, or chronic kidney diseaseassigned to the subject is a likelihood that an event of interest ismore or less likely to occur within 30 days of the time at which thebody fluid sample is obtained from the subject.
 26. A method accordingto claim 6, wherein the increased or decreased likelihood of subsequentacute kidney injury, worsening stage of AKI, mortality, need for renalreplacement therapy, need for withdrawal of renal toxins, end stagerenal disease, heart failure, stroke, myocardial infarction, or chronickidney disease assigned to the subject is a likelihood that an event ofinterest is more or less likely to occur within 72 hours of the time atwhich the body fluid sample is obtained from the subject.
 27. A methodaccording to claim 6, wherein the increased or decreased likelihood ofsubsequent acute kidney injury, worsening stage of AKI, mortality, needfor renal replacement therapy, need for withdrawal of renal toxins, endstage renal disease, heart failure, stroke, myocardial infarction, orchronic kidney disease assigned to the subject is a likelihood that anevent of interest is more or less likely to occur within 24 hours of thetime at which the body fluid sample is obtained from the subject.